fix: sync website color scheme

agents.md

@@ -13,7 +13,7 @@ in the same commit as any change that makes it stale.
   local persistence. No IO except through callers.
 - `crates/ely_servo_host` — Servo embedding, rendering contexts, the
   `ely_servo_sidecar` binary (one Servo process per profile; stdio JSON
-  protocol v3 + macOS IOSurface Mach transport). See
+  protocol v4 + macOS IOSurface Mach transport). See
   `docs/servo-embedding-architecture.md`.
 - `crates/ely_sync_client` — worker API client, device identity/trust,
   E2E snapshot crypto, native-keychain bearer storage, sync-owner store.
@@ -92,6 +92,10 @@ Real and verified:
   profile worker boundary while preserving total device-pixel distance;
   clicks, text, and allow-once permission transfers retain strict ordering.
   Verified by a blocked-worker burst regression and the live-site scroll e2e.
+- Website color scheme: resolved System/Light/Dark state crosses sidecar
+  protocol v4 and reaches `WebView::notify_theme_change`; GPUI appearance
+  events trigger a shell repaint, and first-navigation WebView replacement
+  preserves the selected scheme. Verified with real Servo media-query pixels.
 - Cross-platform: download Open/Reveal use per-OS launchers (macOS `open`,
   Windows `cmd start`/`explorer /select`, Linux `xdg-open`); the command
   overlay closes on Escape.

crates/ely_app/src/services/servo_live.rs

@@ -151,6 +151,7 @@ impl ServoLiveClient {
             height: request.height,
             page_zoom_percent: request.page_zoom_percent,
             device_pixel_ratio: request.device_pixel_ratio,
+            color_scheme: request.color_scheme,
             scroll_delta_x: request.scroll_delta_x,
             scroll_delta_y: request.scroll_delta_y,
             scroll_point_x: request.scroll_point_x,

crates/ely_app/src/services/servo_live_ipc.rs

@@ -256,7 +256,7 @@ mod tests {
     #[test]
     fn reply_rejects_oversized_frame_before_readback_allocation() {
         let header = format!(
-            "{{\"protocol_version\":3,\"error\":null,\"frame\":{{\"loaded_url\":null,\"title\":null,\"state\":\"complete\",\"width\":{0},\"height\":{0},\"device_pixel_ratio\":1.0,\"css_viewport_width\":{0},\"css_viewport_height\":{0},\"rgba_byte_count\":1073741824,\"pixels_changed\":true}}}}\n",
+            "{{\"protocol_version\":4,\"error\":null,\"frame\":{{\"loaded_url\":null,\"title\":null,\"state\":\"complete\",\"width\":{0},\"height\":{0},\"device_pixel_ratio\":1.0,\"css_viewport_width\":{0},\"css_viewport_height\":{0},\"rgba_byte_count\":1073741824,\"pixels_changed\":true}}}}\n",
             MAX_FRAME_DIMENSION
         );
         let mut input = Cursor::new(header.into_bytes());
@@ -269,19 +269,19 @@ mod tests {
 
     #[test]
     fn reply_accepts_the_exact_header_limit() -> Result<(), ServoLiveError> {
-        let mut header = br#"{"protocol_version":3,"error":null,"frame":null}"#.to_vec();
+        let mut header = br#"{"protocol_version":4,"error":null,"frame":null}"#.to_vec();
         header.resize(MAX_RESPONSE_HEADER_BYTES - 1, b' ');
         header.push(b'\n');
 
         let reply = read_reply(&mut Cursor::new(header))?;
 
-        assert_eq!(reply.protocol_version, Some(3));
+        assert_eq!(reply.protocol_version, Some(4));
         Ok(())
     }
 
     #[test]
     fn reply_rejects_one_byte_over_the_header_limit() {
-        let mut header = br#"{"protocol_version":3,"error":null,"frame":null}"#.to_vec();
+        let mut header = br#"{"protocol_version":4,"error":null,"frame":null}"#.to_vec();
         header.resize(MAX_RESPONSE_HEADER_BYTES, b' ');
         header.push(b'\n');
 
@@ -327,7 +327,7 @@ mod tests {
     fn reply_parses_permission_consumption_without_a_frame() -> Result<(), ServoLiveError> {
         let profile_id = ely_domain::ProfileId::new();
         let header = format!(
-            "{{\"protocol_version\":3,\"error\":null,\"frame\":null,\"permission_consumptions\":[{{\"profile_id\":\"{}\",\"origin\":\"https://example.com\",\"feature\":\"camera\",\"grant_revision\":7}}]}}\n",
+            "{{\"protocol_version\":4,\"error\":null,\"frame\":null,\"permission_consumptions\":[{{\"profile_id\":\"{}\",\"origin\":\"https://example.com\",\"feature\":\"camera\",\"grant_revision\":7}}]}}\n",
             profile_id.as_str(),
         );
         let mut input = Cursor::new(header.into_bytes());
@@ -350,7 +350,7 @@ mod tests {
     #[test]
     fn hardware_reply_uses_surface_without_rgba_allocation() -> Result<(), ServoLiveError> {
         let header = concat!(
-            "{\"protocol_version\":3,\"error\":null,",
+            "{\"protocol_version\":4,\"error\":null,",
             "\"surface_handle\":{\"mach_port_name\":91,\"surface_id\":7,\"width\":64,\"height\":48},",
             "\"current_surface_id\":7,",
             "\"frame\":{\"loaded_url\":null,\"title\":null,\"state\":\"complete\",",
@@ -402,7 +402,7 @@ mod tests {
     #[cfg(target_os = "macos")]
     fn hardware_header(current_surface_id: u64, handle_width: u32, handle_height: u32) -> String {
         format!(
-            "{{\"protocol_version\":3,\"error\":null,\"surface_handle\":{{\"mach_port_name\":91,\"surface_id\":7,\"width\":{handle_width},\"height\":{handle_height}}},\"current_surface_id\":{current_surface_id},\"frame\":{{\"loaded_url\":null,\"title\":null,\"state\":\"complete\",\"width\":64,\"height\":48,\"device_pixel_ratio\":1.0,\"css_viewport_width\":64,\"css_viewport_height\":48,\"rgba_byte_count\":0,\"pixels_changed\":true}}}}\n"
+            "{{\"protocol_version\":4,\"error\":null,\"surface_handle\":{{\"mach_port_name\":91,\"surface_id\":7,\"width\":{handle_width},\"height\":{handle_height}}},\"current_surface_id\":{current_surface_id},\"frame\":{{\"loaded_url\":null,\"title\":null,\"state\":\"complete\",\"width\":64,\"height\":48,\"device_pixel_ratio\":1.0,\"css_viewport_width\":64,\"css_viewport_height\":48,\"rgba_byte_count\":0,\"pixels_changed\":true}}}}\n"
         )
     }
 }

crates/ely_app/src/services/servo_live_types.rs

@@ -2,6 +2,7 @@
 use std::sync::Arc;
 use std::{collections::TryReserveError, io, path::PathBuf};
 
+use ely_domain::ColorScheme;
 use serde::Serialize;
 use thiserror::Error;
 
@@ -24,6 +25,7 @@ pub(crate) struct ServoLiveEnsureRequest {
     pub(crate) page_zoom_percent: u16,
     /// Display scale factor used to derive Servo's CSS viewport.
     pub(crate) device_pixel_ratio: f32,
+    pub(crate) color_scheme: ColorScheme,
     pub(crate) scroll_delta_x: i32,
     pub(crate) scroll_delta_y: i32,
     pub(crate) scroll_point_x: Option<u32>,

crates/ely_app/src/services/servo_live_wire.rs

@@ -1,8 +1,9 @@
+use ely_domain::ColorScheme;
 use serde::{Deserialize, Serialize};
 
 use super::ServoLiveSitePermission;
 
-pub(super) const LIVE_PROTOCOL_VERSION: u32 = 3;
+pub(super) const LIVE_PROTOCOL_VERSION: u32 = 4;
 pub(super) const MAX_FRAME_DIMENSION: u32 = 16_384;
 pub(super) const MAX_FRAME_BYTE_COUNT: usize = 256 * 1024 * 1024;
 pub(super) const MAX_RESPONSE_HEADER_BYTES: usize = 256 * 1024;
@@ -22,6 +23,7 @@ pub(super) enum LiveRequest {
         height: u32,
         page_zoom_percent: u16,
         device_pixel_ratio: f32,
+        color_scheme: ColorScheme,
         scroll_delta_x: i32,
         scroll_delta_y: i32,
         scroll_point_x: Option<u32>,

crates/ely_app/src/shell/mod.rs

@@ -136,6 +136,7 @@ pub struct ElyShell {
     pub(crate) local_state_save_scheduled: bool,
     _command_subscription: Subscription,
     _translucency_subscription: Subscription,
+    _appearance_subscription: Subscription,
     _quit_save_subscription: Option<Subscription>,
 }
 
@@ -251,6 +252,8 @@ impl ElyShell {
             }
             ShellState::StartupError(_) => None,
         };
+        let appearance_subscription =
+            cx.observe_window_appearance(window, |_shell, _window, cx| cx.notify());
         let mut shell = Self {
             state,
             focus_handle: cx.focus_handle(),
@@ -307,6 +310,7 @@ impl ElyShell {
             auth_flow_phase: auth::AuthFlowPhase::Idle,
             _command_subscription: command_subscription,
             _translucency_subscription: translucency_subscription,
+            _appearance_subscription: appearance_subscription,
             _quit_save_subscription: None,
         };
         shell._quit_save_subscription = Some(local_persistence::register_quit_save(cx));

crates/ely_app/src/shell/render.rs

@@ -27,35 +27,39 @@ impl Render for ElyShell {
         match &self.state {
             ShellState::Ready(core) => match core.snapshot() {
                 Ok(snapshot) => {
-                    apply_color_mode(
+                    let color_scheme =
-                        resolve_color_mode(snapshot.appearance.theme_mode(), appearance),
+                        resolve_color_scheme(snapshot.appearance.theme_mode(), appearance);
-                        cx,
+                    self.web_surfaces.set_color_scheme(color_scheme);
-                    );
+                    apply_color_scheme(color_scheme, cx);
                     match active_tab_from_snapshot(&snapshot) {
                         Some(active_tab) => self.render_browser(&snapshot, active_tab, window, cx),
                         None => render_error("active tab missing from snapshot".to_string()),
                     }
                 }
                 Err(error) => {
-                    apply_color_mode(
+                    let color_scheme =
-                        resolve_color_mode(ely_domain::ThemeMode::default(), appearance),
+                        resolve_color_scheme(ely_domain::ThemeMode::default(), appearance);
-                        cx,
+                    self.web_surfaces.set_color_scheme(color_scheme);
-                    );
+                    apply_color_scheme(color_scheme, cx);
                     render_error(error.to_string())
                 }
             },
             ShellState::StartupError(message) => {
-                apply_color_mode(
+                let color_scheme =
-                    resolve_color_mode(ely_domain::ThemeMode::default(), appearance),
+                    resolve_color_scheme(ely_domain::ThemeMode::default(), appearance);
-                    cx,
+                self.web_surfaces.set_color_scheme(color_scheme);
-                );
+                apply_color_scheme(color_scheme, cx);
                 render_error(message.clone())
             }
         }
     }
 }
 
-fn apply_color_mode(mode: colors::Mode, cx: &mut Context<ElyShell>) {
+fn apply_color_scheme(color_scheme: ely_domain::ColorScheme, cx: &mut Context<ElyShell>) {
+    let mode = match color_scheme {
+        ely_domain::ColorScheme::Light => colors::Mode::Light,
+        ely_domain::ColorScheme::Dark => colors::Mode::Dark,
+    };
     colors::set_mode(mode);
 
     let component_mode = match mode {
@@ -68,22 +72,19 @@ fn apply_color_mode(mode: colors::Mode, cx: &mut Context<ElyShell>) {
     gpui_component::Theme::global_mut(cx).font_family = SANS_FAMILY.into();
 }
 
-fn resolve_color_mode(
+fn resolve_color_scheme(
     theme_mode: ely_domain::ThemeMode,
     window_appearance: gpui::WindowAppearance,
-) -> colors::Mode {
+) -> ely_domain::ColorScheme {
-    match theme_mode {
+    let system = match window_appearance {
-        ely_domain::ThemeMode::Light => colors::Mode::Light,
-        ely_domain::ThemeMode::Dark => colors::Mode::Dark,
-        ely_domain::ThemeMode::System => match window_appearance {
         gpui::WindowAppearance::Dark | gpui::WindowAppearance::VibrantDark => {
-                colors::Mode::Dark
+            ely_domain::ColorScheme::Dark
         }
         gpui::WindowAppearance::Light | gpui::WindowAppearance::VibrantLight => {
-                colors::Mode::Light
+            ely_domain::ColorScheme::Light
-            }
-        },
         }
+    };
+    theme_mode.resolve(system)
 }
 
 fn active_tab_from_snapshot(snapshot: &BrowserSnapshot) -> Option<&BrowserTab> {
@@ -428,3 +429,31 @@ pub(super) fn tab_profile_label(tab: &BrowserTab, profiles: &[ely_domain::Profil
         .map(|profile| format!("Profile: {}", profile.name()))
         .unwrap_or_else(|| format!("Profile: {}", tab.profile_id().as_str()))
 }
+
+#[cfg(test)]
+mod tests {
+    use ely_domain::{ColorScheme, ThemeMode};
+    use gpui::WindowAppearance;
+
+    use super::resolve_color_scheme;
+
+    #[test]
+    fn resolved_color_scheme_tracks_browser_and_system_modes() {
+        assert_eq!(
+            resolve_color_scheme(ThemeMode::System, WindowAppearance::Dark),
+            ColorScheme::Dark,
+        );
+        assert_eq!(
+            resolve_color_scheme(ThemeMode::System, WindowAppearance::VibrantLight),
+            ColorScheme::Light,
+        );
+        assert_eq!(
+            resolve_color_scheme(ThemeMode::Light, WindowAppearance::Dark),
+            ColorScheme::Light,
+        );
+        assert_eq!(
+            resolve_color_scheme(ThemeMode::Dark, WindowAppearance::Light),
+            ColorScheme::Dark,
+        );
+    }
+}

crates/ely_app/src/shell/web_surface.rs

@@ -1,7 +1,7 @@
 use std::collections::BTreeMap;
 use std::time::{Duration, Instant};
 
-use ely_domain::{BrowserTab, ProfileId, TabId, UrlText};
+use ely_domain::{BrowserTab, ColorScheme, ProfileId, TabId, UrlText};
 
 use crate::services::{ProfileDataMode, servo_live::ServoLivePermissionGrant};
 
@@ -23,16 +23,27 @@ pub(super) struct WebSurfaceStore {
     /// Singleton because only one tab at a time holds keyboard focus
     /// across the whole window. Lives on the store, not per-tab.
     pub(super) keyboard_focus: Option<WebSurfaceKeyboardFocusState>,
+    color_scheme: ColorScheme,
 }
 
 impl WebSurfaceStore {
     pub(super) fn new() -> Self {
-        Self { runtime: WebSurfaceRuntime::new(), surfaces: BTreeMap::new(), keyboard_focus: None }
+        Self {
+            runtime: WebSurfaceRuntime::new(),
+            surfaces: BTreeMap::new(),
+            keyboard_focus: None,
+            color_scheme: ColorScheme::Light,
+        }
     }
 
     #[cfg(test)]
     pub(super) fn new_with_runtime(runtime: WebSurfaceRuntime) -> Self {
-        Self { runtime, surfaces: BTreeMap::new(), keyboard_focus: None }
+        Self {
+            runtime,
+            surfaces: BTreeMap::new(),
+            keyboard_focus: None,
+            color_scheme: ColorScheme::Light,
+        }
     }
 
     #[cfg(test)]
@@ -72,6 +83,7 @@ impl WebSurfaceStore {
             tab.profile_id().clone(),
             profile_data_mode,
             tab.zoom_percent(),
+            self.color_scheme,
             permissions,
         );
         let scope_changed = self.surface_mut(tab.id()).reset_for_scope_change(&ensure_key);
@@ -365,6 +377,11 @@ impl WebSurfaceStore {
         }
     }
 
+    pub(super) fn set_color_scheme(&mut self, color_scheme: ColorScheme) {
+        self.color_scheme = color_scheme;
+        self.runtime.set_color_scheme(color_scheme);
+    }
+
     #[cfg(test)]
     pub(super) fn surface_for_test(&self, tab_id: &TabId) -> Option<&PerTabSurface> {
         self.surfaces.get(tab_id)

crates/ely_app/src/shell/web_surface_runtime.rs

@@ -4,7 +4,7 @@ use std::{
     time::{Duration, Instant},
 };
 
-use ely_domain::{BrowserTab, TabId};
+use ely_domain::{BrowserTab, ColorScheme, TabId};
 
 use crate::services::{
     ProfileDataMode,
@@ -43,6 +43,7 @@ pub(super) struct WebSurfaceRuntime {
     transient_cleanup_error: Option<String>,
     client_factory: LiveRuntimeClientFactory,
     last_generation: u64,
+    color_scheme: ColorScheme,
 }
 
 const SIDECAR_RESTART_BASE_DELAY: Duration = Duration::from_millis(250);
@@ -60,6 +61,7 @@ impl WebSurfaceRuntime {
             transient_cleanup_error,
             client_factory: new_servo_live_client,
             last_generation: 0,
+            color_scheme: ColorScheme::Light,
         }
     }
 
@@ -74,6 +76,7 @@ impl WebSurfaceRuntime {
             transient_cleanup_error: None,
             client_factory,
             last_generation: 0,
+            color_scheme: ColorScheme::Light,
         }
     }
 
@@ -125,6 +128,7 @@ impl WebSurfaceRuntime {
             height: size.height,
             page_zoom_percent: zoom_percent,
             device_pixel_ratio: size.device_pixel_ratio_f32(),
+            color_scheme: self.color_scheme,
             scroll_delta_x,
             scroll_delta_y,
             scroll_point_x,
@@ -226,6 +230,10 @@ impl WebSurfaceRuntime {
         })
     }
 
+    pub(super) fn set_color_scheme(&mut self, color_scheme: ColorScheme) {
+        self.color_scheme = color_scheme;
+    }
+
     pub(super) fn prepare_tab_scope(
         &mut self,
         tab_id: &TabId,
@@ -472,3 +480,6 @@ mod retry_tests;
 #[cfg(test)]
 #[path = "web_surface_runtime_tests.rs"]
 mod tests;
+#[cfg(test)]
+#[path = "web_surface_theme_tests.rs"]
+mod theme_tests;

crates/ely_app/src/shell/web_surface_state.rs

@@ -1,6 +1,6 @@
 use std::time::{Duration, Instant};
 
-use ely_domain::{ProfileId, TabId};
+use ely_domain::{ColorScheme, ProfileId, TabId};
 use gpui::{Bounds, Pixels};
 
 use crate::services::ProfileDataMode;
@@ -309,6 +309,7 @@ pub(super) struct WebSurfaceEnsureKey {
     profile_id: ProfileId,
     profile_data_mode: ProfileDataMode,
     zoom_percent: u16,
+    color_scheme: ColorScheme,
     permissions: Vec<WebSurfaceSitePermission>,
 }
 
@@ -319,6 +320,7 @@ impl WebSurfaceEnsureKey {
         profile_id: ProfileId,
         profile_data_mode: ProfileDataMode,
         zoom_percent: u16,
+        color_scheme: ColorScheme,
         permissions: &[WebSurfaceSitePermission],
     ) -> Self {
         Self {
@@ -327,6 +329,7 @@ impl WebSurfaceEnsureKey {
             profile_id,
             profile_data_mode,
             zoom_percent,
+            color_scheme,
             permissions: permissions.to_vec(),
         }
     }
@@ -446,6 +449,7 @@ mod tests {
             profile_id.clone(),
             ProfileDataMode::Persistent,
             100,
+            ColorScheme::Light,
             &[],
         )
     }

crates/ely_app/src/shell/web_surface_theme_tests.rs

@@ -0,0 +1,73 @@
+use std::sync::Mutex;
+
+use ely_domain::{BrowserTab, ColorScheme, ProfileId, SpaceId, TabId, UrlText};
+use gpui::{Bounds, point, px, size};
+
+use crate::services::{
+    ProfileDataMode,
+    servo_live::{ServoLiveEnsureRequest, ServoLiveFrame},
+};
+
+use super::{
+    super::{
+        web_surface::WebSurfaceStore,
+        web_surface_state::WebSurfaceInputOutcome,
+        web_surface_worker::{LiveRuntimeClient, LiveRuntimeClientError},
+    },
+    WebSurfaceRuntime,
+};
+
+static COLOR_SCHEMES: Mutex<Vec<ColorScheme>> = Mutex::new(Vec::new());
+
+struct ThemeRecordingClient;
+
+impl LiveRuntimeClient for ThemeRecordingClient {
+    fn ensure(
+        &mut self,
+        request: ServoLiveEnsureRequest,
+    ) -> Result<Option<ServoLiveFrame>, LiveRuntimeClientError> {
+        COLOR_SCHEMES
+            .lock()
+            .map_err(|_| "color scheme recorder lock was poisoned".to_string())?
+            .push(request.color_scheme);
+        Ok(None)
+    }
+
+    fn poll(&mut self, _tab_id: String) -> Result<Option<ServoLiveFrame>, LiveRuntimeClientError> {
+        Ok(None)
+    }
+
+    fn close(&mut self, _tab_id: String) -> Result<(), LiveRuntimeClientError> {
+        Ok(())
+    }
+}
+
+#[test]
+fn browser_color_scheme_reaches_each_web_surface_ensure() -> Result<(), String> {
+    COLOR_SCHEMES.lock().map_err(|_| "color scheme recorder lock was poisoned")?.clear();
+    let runtime =
+        WebSurfaceRuntime::new_with_client_factory(|_| Ok(Box::new(ThemeRecordingClient)));
+    let mut store = WebSurfaceStore::new_with_runtime(runtime);
+    let tab = BrowserTab::new(
+        TabId::new(),
+        SpaceId::new(),
+        ProfileId::new(),
+        "Theme",
+        UrlText::parse("https://example.com/theme").map_err(|error| error.to_string())?,
+    );
+    let bounds = Bounds::new(point(px(0.0), px(0.0)), size(px(640.0), px(480.0)));
+
+    assert_eq!(store.record_viewport_size(tab.id(), bounds, 1.0), WebSurfaceInputOutcome::Applied,);
+    let _ = store.ensure_surface(&tab, ProfileDataMode::Transient, &[]);
+    store.flush_runtime_for_test();
+
+    store.set_color_scheme(ColorScheme::Dark);
+    let _ = store.ensure_surface(&tab, ProfileDataMode::Transient, &[]);
+    store.flush_runtime_for_test();
+
+    assert_eq!(
+        *COLOR_SCHEMES.lock().map_err(|_| "color scheme recorder lock was poisoned")?,
+        vec![ColorScheme::Light, ColorScheme::Dark],
+    );
+    Ok(())
+}

crates/ely_app/src/shell/web_surface_worker_dispatch.rs

@@ -25,6 +25,7 @@ pub(super) fn can_merge_consecutive_scroll(
         && latest.height == previous.height
         && latest.page_zoom_percent == previous.page_zoom_percent
         && latest.device_pixel_ratio == previous.device_pixel_ratio
+        && latest.color_scheme == previous.color_scheme
 }
 
 pub(super) fn merge_consecutive_scroll(latest: &mut WorkerRequest, previous: &WorkerRequest) {

crates/ely_app/src/shell/web_surface_worker_scroll_tests.rs

@@ -78,6 +78,7 @@ fn ensure_request(scroll_delta: i32) -> ServoLiveEnsureRequest {
         height: 480,
         page_zoom_percent: 100,
         device_pixel_ratio: 1.0,
+        color_scheme: ely_domain::ColorScheme::Light,
         scroll_delta_x: scroll_delta,
         scroll_delta_y: scroll_delta,
         scroll_point_x: (scroll_delta != 0).then_some(1),

crates/ely_app/src/shell/web_surface_worker_tests.rs

@@ -450,6 +450,7 @@ fn ensure_request(tab_id: &str, input: RecordedInput) -> ServoLiveEnsureRequest
         height: 480,
         page_zoom_percent: 100,
         device_pixel_ratio: 1.0,
+        color_scheme: ely_domain::ColorScheme::Light,
         scroll_delta_x: i32::from(scroll),
         scroll_delta_y: i32::from(scroll),
         scroll_point_x: scroll.then_some(1),

crates/ely_domain/src/appearance.rs

@@ -19,6 +19,24 @@ pub enum ThemeMode {
     Dark,
 }
 
+#[derive(Clone, Copy, Debug, Default, Deserialize, Eq, Ord, PartialEq, PartialOrd, Serialize)]
+#[serde(rename_all = "kebab-case")]
+pub enum ColorScheme {
+    #[default]
+    Light,
+    Dark,
+}
+
+impl ThemeMode {
+    pub fn resolve(self, system: ColorScheme) -> ColorScheme {
+        match self {
+            Self::System => system,
+            Self::Light => ColorScheme::Light,
+            Self::Dark => ColorScheme::Dark,
+        }
+    }
+}
+
 pub const DEFAULT_TRANSLUCENCY_PCT: u8 = 40;
 pub const MAX_TRANSLUCENCY_PCT: u8 = 100;
 
@@ -77,7 +95,7 @@ impl AppearanceSettings {
 
 #[cfg(test)]
 mod tests {
-    use super::{AppearanceSettings, ThemeMode, WallpaperTheme};
+    use super::{AppearanceSettings, ColorScheme, ThemeMode, WallpaperTheme};
 
     #[test]
     fn default_settings_use_dawn_and_system_mode() {
@@ -103,6 +121,13 @@ mod tests {
         assert_eq!(settings.translucency_pct(), 75);
     }
 
+    #[test]
+    fn theme_mode_resolves_explicit_and_system_color_schemes() {
+        assert_eq!(ThemeMode::System.resolve(ColorScheme::Dark), ColorScheme::Dark);
+        assert_eq!(ThemeMode::Light.resolve(ColorScheme::Dark), ColorScheme::Light);
+        assert_eq!(ThemeMode::Dark.resolve(ColorScheme::Light), ColorScheme::Dark);
+    }
+
     #[test]
     fn translucency_setter_clamps_above_max() {
         let mut settings = AppearanceSettings::default();

crates/ely_domain/src/lib.rs

@@ -24,7 +24,8 @@ mod tab_group;
 mod url_text;
 
 pub use appearance::{
-    AppearanceSettings, DEFAULT_TRANSLUCENCY_PCT, MAX_TRANSLUCENCY_PCT, ThemeMode, WallpaperTheme,
+    AppearanceSettings, ColorScheme, DEFAULT_TRANSLUCENCY_PCT, MAX_TRANSLUCENCY_PCT, ThemeMode,
+    WallpaperTheme,
 };
 pub use archive::{ArchiveSource, ArchivedTab};
 pub use bookmark::BookmarkEntry;

crates/ely_servo_host/src/bin/ely_servo_sidecar/live.rs

@@ -21,8 +21,8 @@ use super::{
     },
     live_request::{MAX_REQUEST_LINE_BYTES, RequestLineRead, read_request_line},
     live_session::{
-        LiveInput, LiveSession, apply_input, apply_layout, apply_permissions, bind_profile,
+        LiveInput, LiveSession, apply_color_scheme, apply_input, apply_layout, apply_permissions,
-        ensure_session,
+        bind_profile, ensure_session,
     },
 };
 
@@ -159,6 +159,7 @@ fn handle_request(
             height,
             page_zoom_percent,
             device_pixel_ratio,
+            color_scheme,
             scroll_delta_x,
             scroll_delta_y,
             scroll_point_x,
@@ -184,6 +185,7 @@ fn handle_request(
             let session =
                 ensure_session(host, sessions, tab_id.clone(), &tab, &profile, width, height)?;
             apply_layout(host, session, width, height, page_zoom_percent, device_pixel_ratio)?;
+            apply_color_scheme(host, session, color_scheme)?;
             apply_permissions(
                 host,
                 session,

crates/ely_servo_host/src/bin/ely_servo_sidecar/live_protocol.rs

@@ -1,5 +1,6 @@
 use std::{io, path::PathBuf};
 
+use ely_domain::ColorScheme;
 use ely_servo_host::{
     ConsumedPermission, IOSurfaceHandle, RenderedFrame, ServoHostError, WebViewSnapshot,
     WebViewState,
@@ -10,7 +11,7 @@ use thiserror::Error;
 #[cfg(all(feature = "hardware-render", target_os = "macos"))]
 use super::iosurface_mach::IOSurfaceMachError;
 
-pub(super) const LIVE_PROTOCOL_VERSION: u32 = 3;
+pub(super) const LIVE_PROTOCOL_VERSION: u32 = 4;
 pub(super) const MAX_FRAME_DIMENSION: u32 = 16_384;
 pub(super) const MAX_FRAME_BYTE_COUNT: usize = 256 * 1024 * 1024;
 pub(super) const MAX_RESPONSE_HEADER_BYTES: usize = 256 * 1024;
@@ -35,6 +36,7 @@ pub(super) enum LiveRequest {
         page_zoom_percent: u16,
         #[serde(default = "default_device_pixel_ratio")]
         device_pixel_ratio: f32,
+        color_scheme: ColorScheme,
         #[serde(default)]
         scroll_delta_x: i32,
         #[serde(default)]
@@ -401,7 +403,7 @@ mod tests {
     #[test]
     fn ensure_defaults_optional_input_fields() -> Result<(), serde_json::Error> {
         let request = serde_json::from_str::<LiveRequest>(
-            r#"{"type":"ensure","tab_id":"tab","profile_id":"profile","url":"https://example.com","width":800,"height":600,"site_permission_generation":0}"#,
+            r#"{"type":"ensure","tab_id":"tab","profile_id":"profile","url":"https://example.com","width":800,"height":600,"color_scheme":"dark","site_permission_generation":0}"#,
         )?;
 
         assert!(matches!(
@@ -409,6 +411,7 @@ mod tests {
             LiveRequest::Ensure {
                 page_zoom_percent: 100,
                 device_pixel_ratio: 1.0,
+                color_scheme: ColorScheme::Dark,
                 scroll_delta_x: 0,
                 scroll_delta_y: 0,
                 ready_surface_ids,
@@ -419,19 +422,28 @@ mod tests {
         Ok(())
     }
 
+    #[test]
+    fn ensure_requires_color_scheme() {
+        let request = serde_json::from_str::<LiveRequest>(
+            r#"{"type":"ensure","tab_id":"tab","profile_id":"profile","url":"https://example.com","width":800,"height":600,"site_permission_generation":0}"#,
+        );
+
+        assert!(request.is_err());
+    }
+
     #[test]
     fn handshake_deserializes_protocol_version() -> Result<(), serde_json::Error> {
         let request =
-            serde_json::from_str::<LiveRequest>(r#"{"type":"handshake","protocol_version":3}"#)?;
+            serde_json::from_str::<LiveRequest>(r#"{"type":"handshake","protocol_version":4}"#)?;
 
-        assert!(matches!(request, LiveRequest::Handshake { protocol_version: 3 }));
+        assert!(matches!(request, LiveRequest::Handshake { protocol_version: 4 }));
         Ok(())
     }
 
     #[test]
     fn site_permission_requires_revision() {
         let request = serde_json::from_str::<LiveRequest>(
-            r#"{"type":"ensure","tab_id":"tab","profile_id":"profile","url":"https://example.com","width":800,"height":600,"site_permission_generation":0,"site_permissions":[{"origin":"https://example.com","feature":"camera","state":"allow-once"}]}"#,
+            r#"{"type":"ensure","tab_id":"tab","profile_id":"profile","url":"https://example.com","width":800,"height":600,"color_scheme":"light","site_permission_generation":0,"site_permissions":[{"origin":"https://example.com","feature":"camera","state":"allow-once"}]}"#,
         );
 
         assert!(request.is_err());

crates/ely_servo_host/src/bin/ely_servo_sidecar/live_session.rs

@@ -1,11 +1,11 @@
 use std::collections::{HashMap, hash_map::Entry};
 
-use ely_domain::{ProfileId, TabId, validate_zoom_percent};
+use ely_domain::{ColorScheme, ProfileId, TabId, validate_zoom_percent};
 use ely_servo_host::{
-    HidpiScaleRequest, KeyboardTextRequest, MouseClickRequest, MouseHoverRequest, PageZoomRequest,
+    ColorSchemeRequest, HidpiScaleRequest, KeyboardTextRequest, MouseClickRequest,
-    PermissionDecision, PermissionSnapshotEntry, PermissionSnapshotRequest,
+    MouseHoverRequest, PageZoomRequest, PermissionDecision, PermissionSnapshotEntry,
-    PermissionSnapshotState, RenderedFrame, ResizeRequest, ScrollRequest, ServoHost,
+    PermissionSnapshotRequest, PermissionSnapshotState, RenderedFrame, ResizeRequest,
-    ServoSurfaceSize, SoftwareServoHost,
+    ScrollRequest, ServoHost, ServoSurfaceSize, SoftwareServoHost,
 };
 
 use super::live_protocol::{LiveSidecarError, LiveSitePermission};
@@ -170,6 +170,18 @@ pub(super) fn apply_permissions(
     .map_err(LiveSidecarError::from)
 }
 
+pub(super) fn apply_color_scheme(
+    host: &mut SoftwareServoHost,
+    session: &LiveSession,
+    color_scheme: ColorScheme,
+) -> Result<(), LiveSidecarError> {
+    host.set_color_scheme(ColorSchemeRequest {
+        webview_id: session.webview_id.clone(),
+        color_scheme,
+    })
+    .map_err(LiveSidecarError::from)
+}
+
 pub(super) struct LiveInput {
     pub(super) scroll_delta_x: i32,
     pub(super) scroll_delta_y: i32,

crates/ely_servo_host/src/bin/ely_servo_sidecar/live_tests.rs

@@ -67,7 +67,7 @@ fn request_line_accepts_a_bounded_eof_terminated_frame() -> Result<(), Box<dyn s
 }
 
 fn padded_handshake_line(bytes: usize) -> Vec<u8> {
-    let mut line = br#"{"type":"handshake","protocol_version":3}"#.to_vec();
+    let mut line = br#"{"type":"handshake","protocol_version":4}"#.to_vec();
     assert!(bytes > line.len());
     line.resize(bytes - 1, b' ');
     line.push(b'\n');

crates/ely_servo_host/src/host.rs

@@ -1,5 +1,6 @@
 use ely_domain::{
-    ProfileId, SiteOrigin, SitePermissionDecision, SitePermissionFeature, TabId, UrlText, WebViewId,
+    ColorScheme, ProfileId, SiteOrigin, SitePermissionDecision, SitePermissionFeature, TabId,
+    UrlText, WebViewId,
 };
 
 use crate::ServoHostError;
@@ -280,6 +281,12 @@ pub struct HidpiScaleRequest {
     pub scale_factor: f32,
 }
 
+#[derive(Clone, Debug, Eq, PartialEq)]
+pub struct ColorSchemeRequest {
+    pub webview_id: WebViewId,
+    pub color_scheme: ColorScheme,
+}
+
 #[derive(Clone, Debug, Eq, PartialEq)]
 pub struct MouseClickRequest {
     pub webview_id: WebViewId,
@@ -385,6 +392,8 @@ pub trait ServoHost {
 
     fn set_hidpi_scale(&mut self, request: HidpiScaleRequest) -> Result<(), ServoHostError>;
 
+    fn set_color_scheme(&mut self, request: ColorSchemeRequest) -> Result<(), ServoHostError>;
+
     fn click(&mut self, request: MouseClickRequest) -> Result<(), ServoHostError>;
 
     fn hover(&mut self, request: MouseHoverRequest) -> Result<(), ServoHostError>;

crates/ely_servo_host/src/lib.rs

@@ -22,11 +22,12 @@ pub use error::ServoHostError;
 #[cfg(feature = "hardware-render")]
 pub use hardware_rendering_context::HardwareOffscreenContext;
 pub use host::{
-    ConsumedPermission, HidpiScaleRequest, KeyboardTextRequest, MAX_PAGE_TITLE_BYTES,
+    ColorSchemeRequest, ConsumedPermission, HidpiScaleRequest, KeyboardTextRequest,
-    MouseClickRequest, MouseDragRequest, MouseHoverRequest, NavigationRequest, PageZoomRequest,
+    MAX_PAGE_TITLE_BYTES, MouseClickRequest, MouseDragRequest, MouseHoverRequest,
-    PermissionDecision, PermissionSnapshotEntry, PermissionSnapshotRequest,
+    NavigationRequest, PageZoomRequest, PermissionDecision, PermissionSnapshotEntry,
-    PermissionSnapshotState, RenderedFrame, RenderedFrameSummary, ResizeRequest, ScrollRequest,
+    PermissionSnapshotRequest, PermissionSnapshotState, RenderedFrame, RenderedFrameSummary,
-    ServoHost, TouchTapRequest, WebViewSnapshot, WebViewSnapshotPending, WebViewState,
+    ResizeRequest, ScrollRequest, ServoHost, TouchTapRequest, WebViewSnapshot,
+    WebViewSnapshotPending, WebViewState,
 };
 pub use iosurface_handle::{IOSurfaceHandle, IOSurfaceIdentity};
 #[cfg(feature = "servo-engine")]

crates/ely_servo_host/src/runtime.rs

@@ -9,11 +9,11 @@ use std::{
 };
 
 use dpi::PhysicalSize;
-use ely_domain::{ProfileId, TabId, WebViewId};
+use ely_domain::{ColorScheme, ProfileId, TabId, WebViewId};
 use raw_window_handle::{HasDisplayHandle, HasWindowHandle};
 use servo::{
-    DevicePoint, DeviceVector2D, Opts, Scroll, Servo, ServoBuilder, WebViewBuilder, WebViewPoint,
+    DevicePoint, DeviceVector2D, Opts, Scroll, Servo, ServoBuilder, Theme, WebViewBuilder,
-    WebViewVector,
+    WebViewPoint, WebViewVector,
 };
 
 #[path = "runtime_context.rs"]
@@ -32,8 +32,8 @@ use runtime_preferences::ely_servo_preferences;
 use url::Url;
 
 use crate::{
-    ConsumedPermission, HidpiScaleRequest, KeyboardTextRequest, MouseClickRequest,
+    ColorSchemeRequest, ConsumedPermission, HidpiScaleRequest, KeyboardTextRequest,
-    MouseDragRequest, MouseHoverRequest, NavigationRequest, PageZoomRequest,
+    MouseClickRequest, MouseDragRequest, MouseHoverRequest, NavigationRequest, PageZoomRequest,
     PermissionSnapshotRequest, RenderedFrame, ResizeRequest, ScrollRequest, ServoHost,
     ServoHostError, TouchTapRequest, WebViewSnapshot, WebViewState,
     runtime_input::{
@@ -204,13 +204,15 @@ impl ServoHost for SoftwareServoHost {
         webview.delegate.set_state(WebViewState::Loading);
         if should_create_initial_document {
             let hidpi_scale_factor = webview.webview.hidpi_scale_factor();
-            webview.webview = WebViewBuilder::new(&servo, webview.rendering_context.clone())
+            let replacement = WebViewBuilder::new(&servo, webview.rendering_context.clone())
                 .delegate(webview.delegate.clone())
                 .url(url)
                 // The live path pushes DPR before first navigation. Preserve that scale when
                 // replacing the about:blank WebView so CSS viewport = physical surface / DPR.
                 .hidpi_scale_factor(hidpi_scale_factor)
                 .build();
+            replacement.notify_theme_change(servo_theme(webview.color_scheme));
+            webview.webview = replacement;
             // The input-accepting invariant lives in `webview_for_input`.
             webview.webview.show();
             webview.webview.focus();
@@ -303,6 +305,18 @@ impl ServoHost for SoftwareServoHost {
         Ok(())
     }
 
+    fn set_color_scheme(&mut self, request: ColorSchemeRequest) -> Result<(), ServoHostError> {
+        let webview = self
+            .webviews
+            .get_mut(&request.webview_id)
+            .ok_or_else(|| ServoHostError::WebViewNotFound { id: request.webview_id.clone() })?;
+        if webview.color_scheme != request.color_scheme {
+            webview.color_scheme = request.color_scheme;
+            webview.webview.notify_theme_change(servo_theme(request.color_scheme));
+        }
+        Ok(())
+    }
+
     fn hover(&mut self, request: MouseHoverRequest) -> Result<(), ServoHostError> {
         let webview = self.webview_for_input(&request.webview_id)?;
         send_mouse_hover(&webview.webview, request.x, request.y);
@@ -440,6 +454,7 @@ impl SoftwareServoHost {
                 webview,
                 delegate,
                 requested_url: None,
+                color_scheme: ColorScheme::Light,
             },
         );
 
@@ -472,3 +487,10 @@ impl SoftwareServoHost {
         Ok(webview)
     }
 }
+
+fn servo_theme(color_scheme: ColorScheme) -> Theme {
+    match color_scheme {
+        ColorScheme::Light => Theme::Light,
+        ColorScheme::Dark => Theme::Dark,
+    }
+}

crates/ely_servo_host/src/runtime_webview.rs

@@ -1,6 +1,6 @@
 use std::{cell::Cell, cell::RefCell, rc::Rc};
 
-use ely_domain::{ProfileId, TabId, WebViewId};
+use ely_domain::{ColorScheme, ProfileId, TabId, WebViewId};
 use servo::{LoadStatus, RenderingContext, WebView, WebViewDelegate};
 use url::Url;
 
@@ -19,6 +19,7 @@ pub(super) struct HostWebView {
     pub(super) webview: WebView,
     pub(super) delegate: Rc<HostWebViewDelegate>,
     pub(super) requested_url: Option<String>,
+    pub(super) color_scheme: ColorScheme,
 }
 
 impl HostWebView {

crates/ely_servo_host/tests/sidecar.rs

@@ -208,7 +208,7 @@ fn live_sidecar_drains_an_oversized_request_line_and_recovers_the_handshake()
     let mut stdin = child.stdin.take().ok_or_else(|| io::Error::other("missing stdin"))?;
     let stdout = child.stdout.take().ok_or_else(|| io::Error::other("missing stdout"))?;
     let mut stdout = BufReader::new(stdout);
-    let mut oversized = br#"{"type":"handshake","protocol_version":3}"#.to_vec();
+    let mut oversized = br#"{"type":"handshake","protocol_version":4}"#.to_vec();
     oversized.resize(MAX_REQUEST_LINE_BYTES + 4_096, b' ');
     oversized.push(b'\n');
 

crates/ely_servo_host/tests/sidecar/support.rs

@@ -24,7 +24,7 @@ use super::pages::{
 pub(super) const WIDTH: u32 = 360;
 pub(super) const HEIGHT: u32 = 240;
 pub(super) const RESPONSE_TIMEOUT: Duration = Duration::from_secs(20);
-pub(super) const LIVE_PROTOCOL_VERSION: u32 = 3;
+pub(super) const LIVE_PROTOCOL_VERSION: u32 = 4;
 pub(super) const MAX_FRAME_DIMENSION: u32 = 16_384;
 const MAX_FRAME_BYTE_COUNT: usize = 256 * 1024 * 1024;
 
@@ -38,6 +38,7 @@ pub(super) fn ensure_request(tab_id: &TabId, profile_id: &ProfileId, url: &str)
         "height": HEIGHT,
         "page_zoom_percent": 100,
         "device_pixel_ratio": 1.0,
+        "color_scheme": "light",
         "site_permission_generation": 0,
         "site_permissions": [],
     })

crates/ely_servo_host/tests/software_host.rs

@@ -6,12 +6,13 @@ use std::{
     process::{Command, Stdio},
 };
 
-use ely_domain::{ProfileId, SiteOrigin, SitePermissionFeature, TabId, UrlText};
+use ely_domain::{ColorScheme, ProfileId, SiteOrigin, SitePermissionFeature, TabId, UrlText};
 use ely_servo_host::{
-    HidpiScaleRequest, KeyboardTextRequest, MouseClickRequest, MouseDragRequest, NavigationRequest,
+    ColorSchemeRequest, HidpiScaleRequest, KeyboardTextRequest, MouseClickRequest,
-    PageZoomRequest, PermissionDecision, PermissionSnapshotEntry, PermissionSnapshotRequest,
+    MouseDragRequest, NavigationRequest, PageZoomRequest, PermissionDecision,
-    PermissionSnapshotState, ResizeRequest, ScrollRequest, ServoHost, ServoHostError,
+    PermissionSnapshotEntry, PermissionSnapshotRequest, PermissionSnapshotState, ResizeRequest,
-    ServoSurfaceSize, SoftwareServoHost, TouchTapRequest, WebViewState,
+    ScrollRequest, ServoHost, ServoHostError, ServoSurfaceSize, SoftwareServoHost, TouchTapRequest,
+    WebViewState,
 };
 
 const MINIMUM_CONTENT_PIXELS: u64 = 1_000;
@@ -29,6 +30,7 @@ const CLICK_PROBE_URL: &str = "data:text/html,%3C!doctype%20html%3E%3Ctitle%3ECl
 const DRAG_PROBE_URL: &str = "data:text/html,%3C%21doctype%20html%3E%3Ctitle%3EDrag%20Probe%3C%2Ftitle%3E%3Cstyle%3Ebody%7Bmargin%3A0%3Bbackground%3A%23f6d365%3B%7Dbutton%7Bposition%3Aabsolute%3Bleft%3A80px%3Btop%3A80px%3Bwidth%3A220px%3Bheight%3A90px%3Bfont%3A28px%20sans-serif%3Bbackground%3A%23ffffff%3Bcolor%3A%23111111%3B%7D%3C%2Fstyle%3E%3Cbutton%20id%3Dbox%3EDrag%3C%2Fbutton%3E%3Cscript%3Elet%20dragging%3Dfalse%3Bconst%20box%3Ddocument.getElementById%28%27box%27%29%3BaddEventListener%28%27mousedown%27%2Cevent%3D%3E%7Bif%28event.target%3D%3D%3Dbox%29%7Bdragging%3Dtrue%3B%7D%7D%29%3BaddEventListener%28%27mousemove%27%2Cevent%3D%3E%7Bif%28dragging%26%26event.clientX%3E280%29%7Bdocument.body.style.background%3D%27%230039ff%27%3Bdocument.title%3D%27Dragged%27%3Bbox.textContent%3D%27Dragged%27%3B%7D%7D%29%3BaddEventListener%28%27mouseup%27%2C%28%29%3D%3E%7Bdragging%3Dfalse%3B%7D%29%3B%3C%2Fscript%3E";
 const TOUCH_PROBE_URL: &str = "data:text/html,%3C%21doctype%20html%3E%3Ctitle%3ETouch%20Probe%3C%2Ftitle%3E%3Cstyle%3Ebody%7Bmargin%3A0%3Bbackground%3A%23c7f5d9%3B%7Dbutton%7Bposition%3Aabsolute%3Bleft%3A80px%3Btop%3A80px%3Bwidth%3A220px%3Bheight%3A90px%3Bfont%3A28px%20sans-serif%3Bbackground%3A%23ffffff%3Bcolor%3A%23111111%3Btouch-action%3Amanipulation%3B%7D%3C%2Fstyle%3E%3Cbutton%20ontouchstart%3D%22document.body.dataset.touch%3D%27start%27%3B%22%20onpointerdown%3D%22if%28%21document.body.dataset.pointerType%29%7Bdocument.body.dataset.pointerType%3Devent.pointerType%3B%7D%22%20onclick%3D%22if%28document.body.dataset.pointerType%21%3D%3D%27touch%27%29%7Bdocument.title%3Ddocument.body.dataset.pointerType%3Breturn%3B%7Ddocument.body.style.background%3D%27%230039ff%27%3Bdocument.title%3D%27Touched%27%3Bthis.textContent%3D%27Touched%27%3B%22%3ETap%3C%2Fbutton%3E";
 const TEXT_PROBE_URL: &str = "data:text/html,%3C!doctype%20html%3E%3Ctitle%3EText%20Probe%3C%2Ftitle%3E%3Cstyle%3Ebody%7Bmargin%3A0%3Bbackground%3A%23d9e8ff%3Bfont%3A28px%20sans-serif%3B%7Dinput%7Bposition%3Aabsolute%3Bleft%3A80px%3Btop%3A80px%3Bwidth%3A260px%3Bheight%3A70px%3Bfont%3A28px%20sans-serif%3B%7Doutput%7Bposition%3Aabsolute%3Bleft%3A80px%3Btop%3A180px%3Bfont%3A32px%20sans-serif%3B%7D%3C%2Fstyle%3E%3Cinput%20id%3Dq%20autofocus%20oninput%3D%22document.body.style.background%3D%27%230039ff%27%3Bdocument.getElementById%28%27out%27%29.textContent%3Dthis.value%3B%22%3E%3Coutput%20id%3Dout%3Eempty%3C%2Foutput%3E";
+const THEME_PROBE_URL: &str = "data:text/html,%3C!doctype%20html%3E%3Ctitle%3ETheme%20Probe%3C%2Ftitle%3E%3Cstyle%3Ebody%7Bmargin%3A0%3Bbackground%3A%23f1e2d3%3B%7D%40media%28prefers-color-scheme%3Adark%29%7Bbody%7Bbackground%3A%23112233%3B%7D%7D%3C%2Fstyle%3E";
 const TEXT_PROBE_VALUE: &str = "ely42";
 
 struct PrdSiteCompatibilityCase {
@@ -235,6 +237,29 @@ fn exercise_real_servo_webview_lifecycle() -> Result<(), Box<dyn Error>> {
         "mismatch: {mismatch:?}"
     );
 
+    host.set_color_scheme(ColorSchemeRequest {
+        webview_id: webview_id.clone(),
+        color_scheme: ColorScheme::Dark,
+    })?;
+    host.navigate(NavigationRequest {
+        webview_id: webview_id.clone(),
+        tab_id: tab_id.clone(),
+        url: UrlText::parse(THEME_PROBE_URL)?,
+    })?;
+    wait_for_rendered_webview_with_center_pixel(&mut host, &webview_id, None, [17, 34, 51])?;
+
+    let previous_frame_hash = host.last_rendered_frame()?.sample_hash();
+    host.set_color_scheme(ColorSchemeRequest {
+        webview_id: webview_id.clone(),
+        color_scheme: ColorScheme::Light,
+    })?;
+    wait_for_rendered_webview_with_center_pixel(
+        &mut host,
+        &webview_id,
+        Some(previous_frame_hash),
+        [241, 226, 211],
+    )?;
+
     let url = UrlText::parse(CLICK_PROBE_URL)?;
 
     host.navigate(NavigationRequest { webview_id: webview_id.clone(), tab_id, url })?;

docs/servo-embedding-architecture.md

@@ -50,8 +50,9 @@ transfers the IOSurface send right; the JSON port number is diagnostic metadata.
 
 The protocol supports:
 
-- `handshake`: verify protocol version `3` before accepting browser commands.
+- `handshake`: verify protocol version `4` before accepting browser commands.
-- `ensure`: create or update a WebView, navigation, viewport, zoom, permissions, and input.
+- `ensure`: create or update a WebView, navigation, viewport, zoom, resolved color scheme,
+  permissions, and input.
 - `poll`: advance Servo and return pending frame or metadata state.
 - `close`: destroy one tab's WebView.
 - `shutdown`: acknowledge graceful process shutdown so Servo flushes profile storage.