diff --git a/index.html b/index.html
index 2be2e94..17a7233 100644
--- a/index.html
+++ b/index.html
@@ -5,6 +5,26 @@
     <link rel="icon" type="image/svg+xml" href="/vite.svg" />
     <meta name="viewport" content="width=device-width, initial-scale=1.0" />
     <title>GIT GUD GET ROFLBOX</title>
+    <!-- FOUC prevention: apply color-mode before React hydrates -->
+    <script>
+      (function () {
+        try {
+          var saved = localStorage.getItem('roflbox.colorMode');
+          var mode;
+          if (saved === 'light' || saved === 'dark') {
+            mode = saved;
+          } else if (typeof window.matchMedia === 'function' && window.matchMedia('(prefers-color-scheme: dark)').matches) {
+            mode = 'dark';
+          } else {
+            mode = 'light';
+          }
+          document.documentElement.setAttribute('data-color-mode', mode);
+        } catch (e) {
+          // If localStorage or matchMedia are unavailable, leave the attribute unset
+          // (CSS :root defaults apply).
+        }
+      })();
+    </script>
   </head>
   <body>
     <div id="root"></div>
diff --git a/src/App.tsx b/src/App.tsx
index 7bc36d8..5650053 100644
--- a/src/App.tsx
+++ b/src/App.tsx
@@ -3,6 +3,7 @@ import { Button } from '@/components/ui/button'
 import { Card, CardContent, CardDescription, CardHeader, CardTitle } from '@/components/ui/card'
 import { BackgroundSwitcher } from '@/components/BackgroundSwitcher'
 import { BG_THEMES, DEFAULT_THEME_ID, type BgTheme } from '@/lib/themes'
+import { useColorMode } from '@/lib/colorMode'
 import { TutorialProvider } from '@/components/TutorialProvider'
 import { TutorialOverlay } from '@/components/TutorialOverlay'
 import { useTutorial } from '@/lib/tutorial'
@@ -29,6 +30,9 @@ function App() {
   const [matrixText, setMatrixText] = useState('INITIALIZING...')
   const [chaosMode, setChaosMode] = useState(false)
 
+  // Color mode state – persisted in localStorage under 'roflbox.colorMode'
+  const { preference: colorModePreference, resolvedMode: resolvedColorMode, setColorMode } = useColorMode()
+
   // Background theme state – persisted in localStorage
   const [currentTheme, setCurrentTheme] = useState<BgTheme>(() => {
     const saved = localStorage.getItem(STORAGE_KEY)
@@ -102,8 +106,14 @@ function App() {
         className={`min-h-screen flex flex-col items-center justify-start p-4 relative ${chaosClass('perspective-crazy')}`}
         style={{ overflow: 'visible', background: currentTheme.value }}
       >
-        {/* Background theme switcher */}
-        <BackgroundSwitcher currentThemeId={currentTheme.id} onThemeChange={handleThemeChange} />
+        {/* Background theme + dark mode switcher */}
+        <BackgroundSwitcher
+          currentThemeId={currentTheme.id}
+          onThemeChange={handleThemeChange}
+          colorModePreference={colorModePreference}
+          resolvedColorMode={resolvedColorMode}
+          onColorModeChange={setColorMode}
+        />
       
       {/* FLOATING CHAOS - ABSOLUTE POSITIONED MADNESS - Only in chaos mode */}
       {chaosMode && (
diff --git a/src/components/BackgroundSwitcher.tsx b/src/components/BackgroundSwitcher.tsx
index b1b08e3..48fe226 100644
--- a/src/components/BackgroundSwitcher.tsx
+++ b/src/components/BackgroundSwitcher.tsx
@@ -2,13 +2,23 @@ import { useState } from 'react'
 import { Button } from '@/components/ui/button'
 import { BG_THEMES, type BgTheme } from '@/lib/themes'
 import { useTutorial } from '@/lib/tutorial'
+import { type ColorModePreference, type ColorMode } from '@/lib/colorMode'
 
 interface BackgroundSwitcherProps {
   currentThemeId: string
   onThemeChange: (theme: BgTheme) => void
+  colorModePreference: ColorModePreference
+  resolvedColorMode: ColorMode
+  onColorModeChange: (pref: ColorModePreference) => void
 }
 
-export function BackgroundSwitcher({ currentThemeId, onThemeChange }: BackgroundSwitcherProps) {
+export function BackgroundSwitcher({
+  currentThemeId,
+  onThemeChange,
+  colorModePreference,
+  resolvedColorMode,
+  onColorModeChange,
+}: BackgroundSwitcherProps) {
   const [open, setOpen] = useState(false)
   const { start: startTutorial, completed: tutorialCompleted } = useTutorial()
 
@@ -62,6 +72,43 @@ export function BackgroundSwitcher({ currentThemeId, onThemeChange }: Background
               </button>
             ))}
           </div>
+
+          {/* Color mode selector */}
+          <div className="mt-2 pt-2 border-t border-white/10">
+            <div className="text-white/40 font-mono text-xs mb-1.5 tracking-wider">COLOR MODE:</div>
+            <div
+              role="radiogroup"
+              aria-label="Color mode"
+              className="flex gap-1"
+            >
+              {(['system', 'light', 'dark'] as const).map((pref) => {
+                const labels = { system: 'System', light: 'Light', dark: 'Dark' }
+                const isSelected = colorModePreference === pref
+                return (
+                  <button
+                    key={pref}
+                    role="radio"
+                    aria-checked={isSelected}
+                    aria-label={`${labels[pref]} color mode${pref === 'system' ? ` (currently ${resolvedColorMode})` : ''}`}
+                    onClick={() => onColorModeChange(pref)}
+                    className={`flex-1 text-xs font-mono py-1 rounded transition-colors focus-visible:outline-none focus-visible:ring-2 focus-visible:ring-white/50 ${
+                      isSelected
+                        ? 'bg-white/25 text-white border border-white/40'
+                        : 'text-white/50 hover:text-white/80 hover:bg-white/10 border border-transparent'
+                    }`}
+                  >
+                    {labels[pref]}
+                  </button>
+                )
+              })}
+            </div>
+            {colorModePreference === 'system' && (
+              <div className="text-white/30 font-mono text-xs mt-1">
+                effective: {resolvedColorMode}
+              </div>
+            )}
+          </div>
+
           <div className="mt-2 pt-2 border-t border-white/10">
             <button
               onClick={() => {
diff --git a/src/index.css b/src/index.css
index aa983f6..7ebadc5 100644
--- a/src/index.css
+++ b/src/index.css
@@ -100,6 +100,65 @@
   outline-offset: 2px;
 }
 
+/* =====================================================================
+   Color-mode tokens
+   Applied when data-color-mode="dark|light" is set on <html>.
+   These rules are intentionally placed AFTER all [data-bg-theme] blocks
+   in this file. Both selectors have attribute-selector specificity (0,1,0),
+   so CSS cascade order guarantees the color-mode rules win when both
+   attributes are present on <html> — no combined selector overrides needed.
+
+   Dark mode — coherent dark UI; mirrors the existing :root palette so
+   the default experience is unchanged until the user toggles.
+   ===================================================================== */
+[data-color-mode="dark"] {
+  --text-primary: hsl(120 100% 75%);
+  --text-secondary: hsl(300 70% 80%);
+  --surface-1: hsl(280 80% 12%);
+  --surface-2: hsl(270 100% 8%);
+  --border-color: hsl(300 100% 75%);
+  --button-bg: hsl(320 100% 60%);
+  --button-text: hsl(120 100% 95%);
+}
+
+/* Light mode — readable light surfaces for prolonged use. */
+[data-color-mode="light"] {
+  --text-primary: hsl(240 10% 10%);
+  --text-secondary: hsl(240 5% 40%);
+  --surface-1: hsl(0 0% 98%);
+  --surface-2: hsl(240 5% 93%);
+  --border-color: hsl(240 5% 75%);
+  --button-bg: hsl(240 5% 20%);
+  --button-text: hsl(0 0% 98%);
+
+  /* Override Shadcn/Tailwind design-system HSL tokens so that every
+     component using bg-card, text-card-foreground, text-muted-foreground,
+     border, etc. automatically adapts to the light theme. */
+  --background: 0 0% 96%;
+  --foreground: 240 10% 10%;
+  --card: 0 0% 98%;
+  --card-foreground: 240 10% 10%;
+  --popover: 0 0% 98%;
+  --popover-foreground: 240 10% 10%;
+  --primary: 240 5% 20%;
+  --primary-foreground: 0 0% 98%;
+  --secondary: 240 5% 90%;
+  --secondary-foreground: 240 10% 10%;
+  --muted: 240 5% 90%;
+  --muted-foreground: 240 5% 40%;
+  --accent: 240 5% 85%;
+  --accent-foreground: 240 10% 10%;
+  --border: 240 5% 75%;
+  --input: 0 0% 93%;
+  --ring: 240 5% 30%;
+}
+
+/* Visible focus ring in light mode */
+[data-color-mode="light"] :focus-visible {
+  outline: 2px solid hsl(240 5% 30%);
+  outline-offset: 2px;
+}
+
 @layer utilities {
   .border-rainbow {
     border-image: linear-gradient(45deg, #ff00ff, #00ff00, #ff8000, #ffff00, #00ffff, #ff0080, #8000ff, #ff00ff) 1;
diff --git a/src/lib/colorMode.ts b/src/lib/colorMode.ts
new file mode 100644
index 0000000..c26dff5
--- /dev/null
+++ b/src/lib/colorMode.ts
@@ -0,0 +1,61 @@
+import { useState, useEffect } from 'react'
+
+export type ColorModePreference = 'light' | 'dark' | 'system'
+export type ColorMode = 'light' | 'dark'
+
+const STORAGE_KEY = 'roflbox.colorMode'
+
+function getSystemMode(): ColorMode {
+  return window.matchMedia('(prefers-color-scheme: dark)').matches ? 'dark' : 'light'
+}
+
+function resolveMode(preference: ColorModePreference): ColorMode {
+  if (preference === 'system') return getSystemMode()
+  return preference
+}
+
+/** Apply data-color-mode attribute to <html>. Called both from the hook and
+ *  from the FOUC-prevention inline script in index.html. */
+export function applyColorMode(mode: ColorMode): void {
+  document.documentElement.setAttribute('data-color-mode', mode)
+}
+
+/**
+ * Manages the UI color mode (light / dark / system).
+ *
+ * - Persists the user's explicit choice in localStorage under `roflbox.colorMode`.
+ * - Defaults to `system` (follows `prefers-color-scheme`) when no preference is
+ *   stored yet.
+ * - Applies `data-color-mode="light|dark"` on `document.documentElement` so that
+ *   CSS token overrides in `index.css` take effect.
+ */
+export function useColorMode() {
+  const [preference, setPreference] = useState<ColorModePreference>(() => {
+    const saved = localStorage.getItem(STORAGE_KEY)
+    if (saved === 'light' || saved === 'dark' || saved === 'system') return saved
+    return 'system'
+  })
+
+  const resolvedMode: ColorMode = resolveMode(preference)
+
+  // Keep the attribute in sync whenever the resolved mode changes.
+  useEffect(() => {
+    applyColorMode(resolvedMode)
+  }, [resolvedMode])
+
+  // When the user's preference is "system", listen for OS-level changes.
+  useEffect(() => {
+    if (preference !== 'system') return
+    const mq = window.matchMedia('(prefers-color-scheme: dark)')
+    const handler = () => applyColorMode(getSystemMode())
+    mq.addEventListener('change', handler)
+    return () => mq.removeEventListener('change', handler)
+  }, [preference])
+
+  const setColorMode = (pref: ColorModePreference): void => {
+    setPreference(pref)
+    localStorage.setItem(STORAGE_KEY, pref)
+  }
+
+  return { preference, resolvedMode, setColorMode }
+}
