diff --git a/src/application/policies/color-scheme.js b/src/application/policies/color-scheme.js
new file mode 100644
index 0000000..97e15d6
--- /dev/null
+++ b/src/application/policies/color-scheme.js
@@ -0,0 +1,21 @@
+export const COLOR_SCHEME_PREFERENCES = Object.freeze([
+  "system",
+  "light",
+  "dark",
+]);
+
+/** @param {unknown} value */
+export function normalizeColorSchemePreference(value) {
+  return COLOR_SCHEME_PREFERENCES.includes(/** @type {string} */ (value))
+    ? /** @type {"system" | "light" | "dark"} */ (value)
+    : "system";
+}
+
+/**
+ * @param {"system" | "light" | "dark"} preference
+ * @param {boolean} systemPrefersDark
+ */
+export function resolveColorScheme(preference, systemPrefersDark) {
+  if (preference === "system") return systemPrefersDark ? "dark" : "light";
+  return preference;
+}
diff --git a/src/bootstrap/initialize-color-scheme.js b/src/bootstrap/initialize-color-scheme.js
new file mode 100644
index 0000000..3492cd6
--- /dev/null
+++ b/src/bootstrap/initialize-color-scheme.js
@@ -0,0 +1,36 @@
+import {
+  normalizeColorSchemePreference,
+  resolveColorScheme,
+} from "../application/policies/color-scheme.js";
+
+/**
+ * Applies the persisted public preference before React paints.
+ *
+ * @param {import("../application/ports/storage-port.js").StoragePort} storage
+ * @param {{
+ *   documentElement?: HTMLElement,
+ *   matchMedia?: (query: string) => MediaQueryList
+ * }} [browser]
+ */
+export function initializeColorScheme(storage, browser = {}) {
+  const documentElement = browser.documentElement ?? document.documentElement;
+  const matchMedia =
+    browser.matchMedia ??
+    (typeof window.matchMedia === "function"
+      ? window.matchMedia.bind(window)
+      : () => /** @type {MediaQueryList} */ ({ matches: false }));
+  const stored = storage.read("COLOR_SCHEME");
+  const preference = normalizeColorSchemePreference(
+    stored.ok ? stored.value : undefined,
+  );
+  const resolved = resolveColorScheme(
+    preference,
+    matchMedia("(prefers-color-scheme: dark)").matches,
+  );
+
+  documentElement.dataset.theme = resolved;
+  documentElement.dataset.themePreference = preference;
+  documentElement.style.colorScheme = resolved;
+
+  return Object.freeze({ preference, resolved });
+}
diff --git a/src/bootstrap/main.jsx b/src/bootstrap/main.jsx
index deb5ddc..c6ee9bb 100644
--- a/src/bootstrap/main.jsx
+++ b/src/bootstrap/main.jsx
@@ -5,6 +5,7 @@ import { QueryClientProvider } from "@tanstack/react-query";
 import { BootErrorShell } from "../presentation/boundaries/boot-error-shell.jsx";
 import { AppRouter } from "../presentation/routes/app-router.jsx";
 import { createRuntimeComposition } from "./create-runtime-composition.js";
+import { initializeColorScheme } from "./initialize-color-scheme.js";
 import { BootConfigError } from "./load-runtime-config.js";
 import { ReleaseManifestError } from "./load-release-manifest.js";
 import "../presentation/styles/theme.css";
@@ -20,6 +21,7 @@ const root = createRoot(rootElement);
 async function boot() {
   try {
     const composition = await createRuntimeComposition();
+    initializeColorScheme(composition.ports.storage);
     root.render(
       <StrictMode>
         <QueryClientProvider client={composition.ports.queryClient}>
@@ -27,6 +29,7 @@ async function boot() {
             authSession={composition.ports.authSession}
             basename={composition.config.build.routerBasePath}
             buildId={composition.release.buildId}
+            storage={composition.ports.storage}
             telemetry={composition.ports.telemetry}
           />
         </QueryClientProvider>
diff --git a/src/presentation/layouts/app-shell.jsx b/src/presentation/layouts/app-shell.jsx
index 35f70d6..6147dd7 100644
--- a/src/presentation/layouts/app-shell.jsx
+++ b/src/presentation/layouts/app-shell.jsx
@@ -3,6 +3,7 @@ import { NavLink, Outlet, useLocation } from "react-router-dom";
 
 import { NAVIGATION_ROUTES, routePath } from "../../contracts/routes.js";
 import { useSession } from "../providers/session-provider.jsx";
+import { useTheme } from "../providers/theme-provider.jsx";
 
 const SESSION_LABELS = Object.freeze({
   authenticated: "인증됨",
@@ -14,6 +15,7 @@ const SESSION_LABELS = Object.freeze({
 export function AppShell() {
   const location = useLocation();
   const { sessionState, beginSignIn, signOut, recover } = useSession();
+  const { preference, setPreference } = useTheme();
   const [navigationOpen, setNavigationOpen] = useState(false);
   const [sessionActionPending, setSessionActionPending] = useState(false);
   const [sessionActionFailed, setSessionActionFailed] = useState(false);
@@ -80,6 +82,25 @@ export function AppShell() {
           Frontend Skeleton
         </NavLink>
         <div className="app-shell__session">
+          <label className="visually-hidden" htmlFor="theme-preference">
+            색상 테마
+          </label>
+          <select
+            className="theme-selector"
+            id="theme-preference"
+            value={preference}
+            onChange={(event) =>
+              setPreference(
+                /** @type {"system" | "light" | "dark"} */ (
+                  event.currentTarget.value
+                ),
+              )
+            }
+          >
+            <option value="system">시스템 테마</option>
+            <option value="light">라이트 테마</option>
+            <option value="dark">다크 테마</option>
+          </select>
           <span className="session-status" data-state={sessionState}>
             {SESSION_LABELS[sessionState]}
           </span>
diff --git a/src/presentation/providers/theme-provider.jsx b/src/presentation/providers/theme-provider.jsx
new file mode 100644
index 0000000..eb181f7
--- /dev/null
+++ b/src/presentation/providers/theme-provider.jsx
@@ -0,0 +1,86 @@
+import {
+  createContext,
+  useContext,
+  useEffect,
+  useLayoutEffect,
+  useMemo,
+  useState,
+} from "react";
+
+import {
+  normalizeColorSchemePreference,
+  resolveColorScheme,
+} from "../../application/policies/color-scheme.js";
+
+/**
+ * @typedef {{
+ *   preference: "system" | "light" | "dark",
+ *   resolvedTheme: "light" | "dark",
+ *   setPreference: (preference: "system" | "light" | "dark") => void
+ * }} ThemeContextValue
+ */
+
+const ThemeContext = createContext(/** @type {ThemeContextValue | null} */ (null));
+
+function systemPrefersDark() {
+  return (
+    typeof window.matchMedia === "function" &&
+    window.matchMedia("(prefers-color-scheme: dark)").matches
+  );
+}
+
+/**
+ * @param {{
+ *   storage?: import("../../application/ports/storage-port.js").StoragePort,
+ *   children: React.ReactNode
+ * }} props
+ */
+export function ThemeProvider({ storage, children }) {
+  const [preference, updatePreference] = useState(() => {
+    const result = storage?.read("COLOR_SCHEME");
+    return normalizeColorSchemePreference(
+      result?.ok ? result.value : undefined,
+    );
+  });
+  const [darkSystemTheme, setDarkSystemTheme] = useState(systemPrefersDark);
+  const resolvedTheme = resolveColorScheme(preference, darkSystemTheme);
+
+  useEffect(() => {
+    if (typeof window.matchMedia !== "function") return undefined;
+    const query = window.matchMedia("(prefers-color-scheme: dark)");
+    /** @param {MediaQueryListEvent} event */
+    const update = (event) => setDarkSystemTheme(event.matches);
+    setDarkSystemTheme(query.matches);
+    query.addEventListener("change", update);
+    return () => query.removeEventListener("change", update);
+  }, []);
+
+  useLayoutEffect(() => {
+    document.documentElement.dataset.theme = resolvedTheme;
+    document.documentElement.dataset.themePreference = preference;
+    document.documentElement.style.colorScheme = resolvedTheme;
+  }, [preference, resolvedTheme]);
+
+  const value = useMemo(
+    () =>
+      Object.freeze({
+        preference,
+        resolvedTheme,
+        /** @param {"system" | "light" | "dark"} next */
+        setPreference(next) {
+          const normalized = normalizeColorSchemePreference(next);
+          updatePreference(normalized);
+          storage?.write("COLOR_SCHEME", normalized);
+        },
+      }),
+    [preference, resolvedTheme, storage],
+  );
+
+  return <ThemeContext.Provider value={value}>{children}</ThemeContext.Provider>;
+}
+
+export function useTheme() {
+  const theme = useContext(ThemeContext);
+  if (!theme) throw new Error("ThemeProvider is required");
+  return theme;
+}
diff --git a/src/presentation/routes/app-router.jsx b/src/presentation/routes/app-router.jsx
index 8cfc004..d7727a9 100644
--- a/src/presentation/routes/app-router.jsx
+++ b/src/presentation/routes/app-router.jsx
@@ -11,6 +11,7 @@ import { RouteBoundary } from "../boundaries/render-error-boundary.jsx";
 import { AppShell } from "../layouts/app-shell.jsx";
 import { PageHeader } from "../components/page-header.jsx";
 import { SessionProvider, useSession } from "../providers/session-provider.jsx";
+import { ThemeProvider } from "../providers/theme-provider.jsx";
 import { decideRouteAccess } from "./navigation-policy.js";
 
 const HomePage = lazy(() => import("../pages/home-page.jsx"));
@@ -171,6 +172,7 @@ function PublicRoute({ routeId, buildId, telemetry, children }) {
  *   authSession: import("../../application/ports/auth-session-port.js").AuthSessionPort,
  *   basename?: string,
  *   buildId?: string,
+ *   storage?: import("../../application/ports/storage-port.js").StoragePort,
  *   telemetry?: import("../../application/ports/telemetry-port.js").TelemetryPort
  * }} props
  */
@@ -178,13 +180,15 @@ export function AppRouter({
   authSession,
   basename = "/",
   buildId = "local-build",
+  storage,
   telemetry,
 }) {
   return (
     <BrowserRouter basename={basename}>
-      <SessionProvider authSession={authSession}>
-        <Routes>
-          <Route element={<AppShell />}>
+      <ThemeProvider storage={storage}>
+        <SessionProvider authSession={authSession}>
+          <Routes>
+            <Route element={<AppShell />}>
             <Route
               index
               element={
@@ -259,9 +263,10 @@ export function AppRouter({
                 </PublicRoute>
               }
             />
-          </Route>
-        </Routes>
-      </SessionProvider>
+            </Route>
+          </Routes>
+        </SessionProvider>
+      </ThemeProvider>
     </BrowserRouter>
   );
 }
diff --git a/src/presentation/styles/theme.css b/src/presentation/styles/theme.css
index 8b9eebf..7653fe8 100644
--- a/src/presentation/styles/theme.css
+++ b/src/presentation/styles/theme.css
@@ -3,12 +3,28 @@
 @theme {
   --color-surface: oklch(0.985 0.003 247);
   --color-surface-muted: oklch(0.94 0.01 247);
+  --color-panel: oklch(1 0 0);
+  --color-border: oklch(0.87 0.015 247);
   --color-content: oklch(0.25 0.025 247);
   --color-content-muted: oklch(0.48 0.025 247);
   --color-action: oklch(0.55 0.18 255);
   --color-action-hover: oklch(0.48 0.2 255);
   --color-danger: oklch(0.55 0.2 25);
+  --color-danger-hover: oklch(0.47 0.2 25);
+  --color-on-action: oklch(1 0 0);
   --color-focus: oklch(0.72 0.16 225);
+  --color-info-content: oklch(0.38 0.16 255);
+  --color-info-surface: oklch(0.95 0.03 255);
+  --color-info-border: oklch(0.75 0.08 250);
+  --color-success-content: oklch(0.35 0.12 155);
+  --color-success-surface: oklch(0.95 0.04 155);
+  --color-success-border: oklch(0.72 0.1 155);
+  --color-warning-content: oklch(0.38 0.12 70);
+  --color-warning-surface: oklch(0.96 0.05 80);
+  --color-warning-border: oklch(0.75 0.12 80);
+  --color-danger-content: oklch(0.42 0.18 25);
+  --color-danger-surface: oklch(0.96 0.035 25);
+  --color-danger-border: oklch(0.72 0.12 25);
   --radius-control: 0.5rem;
   --radius-surface: 0.75rem;
   --spacing-page: 1.5rem;
@@ -22,6 +38,33 @@
     font-family: var(--font-sans);
   }
 
+  :root[data-theme="dark"] {
+    --color-surface: oklch(0.16 0.02 255);
+    --color-surface-muted: oklch(0.25 0.025 255);
+    --color-panel: oklch(0.205 0.022 255);
+    --color-border: oklch(0.36 0.025 255);
+    --color-content: oklch(0.94 0.012 255);
+    --color-content-muted: oklch(0.74 0.025 255);
+    --color-action: oklch(0.7 0.14 250);
+    --color-action-hover: oklch(0.79 0.12 245);
+    --color-danger: oklch(0.68 0.19 25);
+    --color-danger-hover: oklch(0.76 0.16 25);
+    --color-on-action: oklch(0.16 0.02 255);
+    --color-focus: oklch(0.82 0.15 220);
+    --color-info-content: oklch(0.83 0.09 250);
+    --color-info-surface: oklch(0.27 0.045 255);
+    --color-info-border: oklch(0.55 0.09 250);
+    --color-success-content: oklch(0.83 0.1 155);
+    --color-success-surface: oklch(0.27 0.045 155);
+    --color-success-border: oklch(0.53 0.1 155);
+    --color-warning-content: oklch(0.88 0.1 80);
+    --color-warning-surface: oklch(0.29 0.045 80);
+    --color-warning-border: oklch(0.58 0.11 80);
+    --color-danger-content: oklch(0.84 0.11 25);
+    --color-danger-surface: oklch(0.28 0.055 25);
+    --color-danger-border: oklch(0.56 0.13 25);
+  }
+
   body {
     margin: 0;
     min-width: 20rem;
@@ -81,7 +124,7 @@
     left: 0.75rem;
     padding: 0.75rem 1rem;
     border-radius: var(--radius-control);
-    color: white;
+    color: var(--color-panel);
     background: var(--color-content);
     transform: translateY(-200%);
   }
@@ -111,7 +154,7 @@
     min-width: 0;
     padding: 0.75rem 1.25rem;
     border-bottom: 1px solid var(--color-surface-muted);
-    background: color-mix(in oklch, white 92%, var(--color-surface));
+    background: color-mix(in oklch, var(--color-panel) 92%, var(--color-surface));
     box-shadow: 0 1px 8px color-mix(in oklch, var(--color-content) 8%, transparent);
   }
 
@@ -132,7 +175,7 @@
     border-radius: var(--radius-control);
     padding: 0.55rem 0.75rem;
     color: var(--color-content);
-    background: white;
+    background: var(--color-panel);
     cursor: pointer;
   }
 
@@ -143,13 +186,24 @@
     margin-inline-start: auto;
   }
 
+  .theme-selector {
+    min-height: 2.25rem;
+    max-width: 8.5rem;
+    border: 1px solid var(--color-border);
+    border-radius: var(--radius-control);
+    padding: 0.35rem 2rem 0.35rem 0.65rem;
+    color: var(--color-content);
+    background: var(--color-panel);
+    cursor: pointer;
+  }
+
   .app-shell__session-error {
     position: absolute;
     top: calc(100% + 0.25rem);
     right: 1rem;
     padding: 0.5rem;
     color: var(--color-danger);
-    background: white;
+    background: var(--color-panel);
   }
 
   .session-status {
@@ -165,8 +219,8 @@
   }
 
   .session-status[data-state="authenticated"] {
-    color: oklch(0.35 0.12 155);
-    background: oklch(0.93 0.05 155);
+    color: var(--color-success-content);
+    background: var(--color-success-surface);
   }
 
   .session-status[data-state="integration-failed"] {
@@ -179,8 +233,8 @@
     grid-area: sidebar;
     height: calc(100vh - 4.5rem);
     padding: 1.25rem 0.75rem;
-    border-right: 1px solid var(--color-surface-muted);
-    background: white;
+    border-right: 1px solid var(--color-border);
+    background: var(--color-panel);
   }
 
   .app-navigation {
@@ -208,7 +262,11 @@
 
   .app-navigation__link.is-active {
     color: var(--color-action-hover);
-    background: color-mix(in oklch, var(--color-action) 10%, white);
+    background: color-mix(
+      in oklch,
+      var(--color-action) 14%,
+      var(--color-panel)
+    );
     font-weight: 800;
   }
 
@@ -224,16 +282,19 @@
   }
 
   .ui-panel {
-    @apply rounded-surface border border-surface-muted bg-white p-6 shadow-sm;
+    @apply rounded-surface p-6 shadow-sm;
+    border: 1px solid var(--color-border);
+    background: var(--color-panel);
   }
 
   .ui-button {
-    @apply rounded-control bg-action px-4 py-2 font-semibold text-white;
+    @apply rounded-control bg-action px-4 py-2 font-semibold;
     display: inline-flex;
     min-height: 2.75rem;
     align-items: center;
     justify-content: center;
     border: 0;
+    color: var(--color-on-action);
     text-decoration: none;
     cursor: pointer;
   }
@@ -250,7 +311,7 @@
   .ui-button--secondary {
     border: 1px solid var(--color-surface-muted);
     color: var(--color-content);
-    background: white;
+    background: var(--color-panel);
   }
 
   .ui-button--secondary:hover {
@@ -259,12 +320,12 @@
   }
 
   .ui-button--danger {
-    color: white;
+    color: var(--color-on-action);
     background: var(--color-danger);
   }
 
   .ui-button--danger:hover {
-    background: oklch(0.47 0.2 25);
+    background: var(--color-danger-hover);
   }
 
   .ui-button--ghost {
@@ -321,11 +382,12 @@
     width: 100%;
     min-height: 2.75rem;
     box-sizing: border-box;
-    border: 1px solid color-mix(in oklch, var(--color-content-muted) 55%, white);
+    border: 1px solid
+      color-mix(in oklch, var(--color-content-muted) 55%, var(--color-panel));
     border-radius: var(--radius-control);
     padding: 0.65rem 0.8rem;
     color: var(--color-content);
-    background: white;
+    background: var(--color-panel);
   }
 
   .ui-field__input[aria-invalid="true"] {
@@ -337,10 +399,10 @@
     min-width: 0;
     flex-direction: column;
     gap: 1.25rem;
-    border: 1px solid var(--color-surface-muted);
+    border: 1px solid var(--color-border);
     border-radius: var(--radius-surface);
     padding: 1.25rem;
-    background: white;
+    background: var(--color-panel);
     box-shadow: 0 8px 28px color-mix(in oklch, var(--color-content) 6%, transparent);
   }
 
@@ -376,23 +438,23 @@
   }
 
   .ui-alert--info {
-    border-color: oklch(0.75 0.08 250);
-    background: oklch(0.96 0.025 250);
+    border-color: var(--color-info-border);
+    background: var(--color-info-surface);
   }
 
   .ui-alert--success {
-    border-color: oklch(0.72 0.1 155);
-    background: oklch(0.96 0.03 155);
+    border-color: var(--color-success-border);
+    background: var(--color-success-surface);
   }
 
   .ui-alert--warning {
-    border-color: oklch(0.75 0.12 80);
-    background: oklch(0.97 0.035 80);
+    border-color: var(--color-warning-border);
+    background: var(--color-warning-surface);
   }
 
   .ui-alert--danger {
-    border-color: oklch(0.72 0.12 25);
-    background: oklch(0.96 0.03 25);
+    border-color: var(--color-danger-border);
+    background: var(--color-danger-surface);
   }
 
   .ui-alert__content,
@@ -432,23 +494,23 @@
   }
 
   .ui-badge--info {
-    color: oklch(0.38 0.16 255);
-    background: oklch(0.93 0.04 255);
+    color: var(--color-info-content);
+    background: var(--color-info-surface);
   }
 
   .ui-badge--success {
-    color: oklch(0.35 0.12 155);
-    background: oklch(0.93 0.05 155);
+    color: var(--color-success-content);
+    background: var(--color-success-surface);
   }
 
   .ui-badge--warning {
-    color: oklch(0.38 0.12 70);
-    background: oklch(0.94 0.06 80);
+    color: var(--color-warning-content);
+    background: var(--color-warning-surface);
   }
 
   .ui-badge--danger {
-    color: oklch(0.42 0.18 25);
-    background: oklch(0.94 0.045 25);
+    color: var(--color-danger-content);
+    background: var(--color-danger-surface);
   }
 
   .ui-dialog {
@@ -460,7 +522,7 @@
     border-radius: var(--radius-surface);
     padding: 0;
     color: var(--color-content);
-    background: white;
+    background: var(--color-panel);
     box-shadow: 0 24px 70px color-mix(in oklch, var(--color-content) 25%, transparent);
   }
 
@@ -508,6 +570,10 @@
     padding-block: clamp(1rem, 5vw, 3.5rem) 0.5rem;
   }
 
+  [data-route-heading]:focus {
+    outline: none;
+  }
+
   .page-header__eyebrow {
     margin-block-end: 0.75rem;
     color: var(--color-action);
@@ -612,10 +678,10 @@
     display: grid;
     gap: 0.45rem;
     min-width: 0;
-    border: 1px solid var(--color-surface-muted);
+    border: 1px solid var(--color-border);
     border-radius: var(--radius-control);
     padding: 0.75rem;
-    background: white;
+    background: var(--color-panel);
   }
 
   .token-swatch__color {
@@ -633,9 +699,6 @@
   }
 
   .gallery-notice {
-    position: sticky;
-    z-index: 10;
-    bottom: 1rem;
     display: block;
     width: fit-content;
     max-width: 100%;
@@ -644,7 +707,7 @@
     border-radius: 999px;
     padding: 0.65rem 1rem;
     color: var(--color-content);
-    background: white;
+    background: var(--color-panel);
     box-shadow: 0 8px 28px color-mix(in oklch, var(--color-content) 10%, transparent);
     font-size: 0.875rem;
     font-weight: 650;
@@ -681,14 +744,14 @@
   }
 
   .state-surface--warning {
-    border-color: oklch(0.75 0.12 80);
-    background: oklch(0.97 0.035 80);
+    border-color: var(--color-warning-border);
+    background: var(--color-warning-surface);
   }
 
   .state-surface--danger,
   .ui-terminal-error {
-    border-color: oklch(0.72 0.12 25);
-    background: oklch(0.98 0.02 25);
+    border-color: var(--color-danger-border);
+    background: var(--color-danger-surface);
   }
 
   .state-surface--loading {
@@ -757,6 +820,10 @@
     display: none;
   }
 
+  .app-shell__brand {
+    display: none;
+  }
+
   .readiness-grid {
     grid-template-columns: minmax(0, 1fr);
   }
diff --git a/tests/e2e/theme.spec.js b/tests/e2e/theme.spec.js
new file mode 100644
index 0000000..1f4ff4a
--- /dev/null
+++ b/tests/e2e/theme.spec.js
@@ -0,0 +1,38 @@
+import AxeBuilder from "@axe-core/playwright";
+import { expect, test } from "@playwright/test";
+
+test("persists an explicit color scheme through the storage contract", async ({
+  page,
+}) => {
+  await page.goto("/");
+  const selector = page.getByRole("combobox", { name: "색상 테마" });
+
+  await selector.selectOption("dark");
+  await expect(page.locator("html")).toHaveAttribute("data-theme", "dark");
+  await expect(page.locator("html")).toHaveCSS("color-scheme", "dark");
+  const results = await new AxeBuilder({ page })
+    .withTags(["wcag2a", "wcag2aa", "wcag21a", "wcag21aa"])
+    .analyze();
+  expect(
+    results.violations.filter((violation) =>
+      ["critical", "serious"].includes(violation.impact ?? ""),
+    ),
+  ).toEqual([]);
+
+  await page.reload();
+  await expect(selector).toHaveValue("dark");
+  await expect(page.locator("html")).toHaveAttribute("data-theme", "dark");
+});
+
+test("tracks operating-system changes while system preference is selected", async ({
+  page,
+}) => {
+  await page.emulateMedia({ colorScheme: "dark" });
+  await page.goto("/");
+  const selector = page.getByRole("combobox", { name: "색상 테마" });
+  await selector.selectOption("system");
+  await expect(page.locator("html")).toHaveAttribute("data-theme", "dark");
+
+  await page.emulateMedia({ colorScheme: "light" });
+  await expect(page.locator("html")).toHaveAttribute("data-theme", "light");
+});
diff --git a/tests/unit/color-scheme.test.js b/tests/unit/color-scheme.test.js
new file mode 100644
index 0000000..065aa96
--- /dev/null
+++ b/tests/unit/color-scheme.test.js
@@ -0,0 +1,44 @@
+// @vitest-environment jsdom
+
+import { describe, expect, it } from "vitest";
+
+import {
+  normalizeColorSchemePreference,
+  resolveColorScheme,
+} from "../../src/application/policies/color-scheme.js";
+import { initializeColorScheme } from "../../src/bootstrap/initialize-color-scheme.js";
+
+describe("color scheme policy", () => {
+  it("normalizes unknown persisted values to the safe system default", () => {
+    expect(normalizeColorSchemePreference("sepia")).toBe("system");
+    expect(normalizeColorSchemePreference("dark")).toBe("dark");
+  });
+
+  it("resolves system and explicit preferences deterministically", () => {
+    expect(resolveColorScheme("system", true)).toBe("dark");
+    expect(resolveColorScheme("system", false)).toBe("light");
+    expect(resolveColorScheme("light", true)).toBe("light");
+  });
+
+  it("applies a persisted preference before application paint", () => {
+    const storage = {
+      read: () => ({ ok: true, value: "system" }),
+      write: () => ({ ok: true }),
+      remove: () => ({ ok: true }),
+    };
+
+    const result = initializeColorScheme(storage, {
+      documentElement: document.documentElement,
+      matchMedia: () =>
+        /** @type {MediaQueryList} */ ({ matches: true }),
+    });
+
+    expect(result).toEqual({ preference: "system", resolved: "dark" });
+    expect(document.documentElement).toHaveAttribute("data-theme", "dark");
+    expect(document.documentElement).toHaveAttribute(
+      "data-theme-preference",
+      "system",
+    );
+    expect(document.documentElement.style.colorScheme).toBe("dark");
+  });
+});