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+# Color Systems Reference
+
+## Color Palette Generation
+
+### Perceptually Uniform Scales
+
+Using OKLCH for perceptually uniform color scales:
+
+```css
+/* OKLCH: Lightness, Chroma, Hue */
+:root {
+  /* Generate a blue scale with consistent perceived lightness steps */
+  --blue-50: oklch(97% 0.02 250);
+  --blue-100: oklch(93% 0.04 250);
+  --blue-200: oklch(86% 0.08 250);
+  --blue-300: oklch(75% 0.12 250);
+  --blue-400: oklch(65% 0.16 250);
+  --blue-500: oklch(55% 0.2 250); /* Primary */
+  --blue-600: oklch(48% 0.18 250);
+  --blue-700: oklch(40% 0.16 250);
+  --blue-800: oklch(32% 0.12 250);
+  --blue-900: oklch(25% 0.08 250);
+  --blue-950: oklch(18% 0.05 250);
+}
+```
+
+### Programmatic Scale Generation
+
+```tsx
+function generateColorScale(
+  hue: number,
+  saturation: number = 100,
+): Record<string, string> {
+  const lightnessStops = [
+    { name: "50", l: 97 },
+    { name: "100", l: 93 },
+    { name: "200", l: 85 },
+    { name: "300", l: 75 },
+    { name: "400", l: 65 },
+    { name: "500", l: 55 },
+    { name: "600", l: 45 },
+    { name: "700", l: 35 },
+    { name: "800", l: 25 },
+    { name: "900", l: 18 },
+    { name: "950", l: 12 },
+  ];
+
+  return Object.fromEntries(
+    lightnessStops.map(({ name, l }) => [
+      name,
+      `hsl(${hue}, ${saturation}%, ${l}%)`,
+    ]),
+  );
+}
+
+// Generate semantic colors
+const brand = generateColorScale(220); // Blue
+const success = generateColorScale(142); // Green
+const warning = generateColorScale(38); // Amber
+const error = generateColorScale(0); // Red
+```
+
+## Semantic Color Tokens
+
+### Two-Tier Token System
+
+```css
+/* Tier 1: Primitive colors (raw values) */
+:root {
+  --primitive-blue-500: #3b82f6;
+  --primitive-blue-600: #2563eb;
+  --primitive-green-500: #22c55e;
+  --primitive-red-500: #ef4444;
+  --primitive-gray-50: #f9fafb;
+  --primitive-gray-900: #111827;
+}
+
+/* Tier 2: Semantic tokens (purpose-based) */
+:root {
+  /* Background */
+  --color-bg-primary: var(--primitive-gray-50);
+  --color-bg-secondary: white;
+  --color-bg-tertiary: var(--primitive-gray-100);
+  --color-bg-inverse: var(--primitive-gray-900);
+
+  /* Text */
+  --color-text-primary: var(--primitive-gray-900);
+  --color-text-secondary: var(--primitive-gray-600);
+  --color-text-tertiary: var(--primitive-gray-400);
+  --color-text-inverse: white;
+  --color-text-link: var(--primitive-blue-600);
+
+  /* Border */
+  --color-border-default: var(--primitive-gray-200);
+  --color-border-strong: var(--primitive-gray-300);
+  --color-border-focus: var(--primitive-blue-500);
+
+  /* Interactive */
+  --color-interactive-primary: var(--primitive-blue-600);
+  --color-interactive-primary-hover: var(--primitive-blue-700);
+  --color-interactive-primary-active: var(--primitive-blue-800);
+
+  /* Status */
+  --color-status-success: var(--primitive-green-500);
+  --color-status-warning: var(--primitive-amber-500);
+  --color-status-error: var(--primitive-red-500);
+  --color-status-info: var(--primitive-blue-500);
+}
+```
+
+### Component Tokens
+
+```css
+/* Tier 3: Component-specific tokens */
+:root {
+  /* Button */
+  --button-bg: var(--color-interactive-primary);
+  --button-bg-hover: var(--color-interactive-primary-hover);
+  --button-text: white;
+  --button-border-radius: 0.375rem;
+
+  /* Input */
+  --input-bg: var(--color-bg-secondary);
+  --input-border: var(--color-border-default);
+  --input-border-focus: var(--color-border-focus);
+  --input-text: var(--color-text-primary);
+  --input-placeholder: var(--color-text-tertiary);
+
+  /* Card */
+  --card-bg: var(--color-bg-secondary);
+  --card-border: var(--color-border-default);
+  --card-shadow: 0 1px 3px rgba(0, 0, 0, 0.1);
+}
+```
+
+## Dark Mode Implementation
+
+### CSS Custom Properties Approach
+
+```css
+/* Light theme (default) */
+:root {
+  --color-bg-primary: #ffffff;
+  --color-bg-secondary: #f9fafb;
+  --color-bg-tertiary: #f3f4f6;
+  --color-text-primary: #111827;
+  --color-text-secondary: #4b5563;
+  --color-border-default: #e5e7eb;
+}
+
+/* Dark theme */
+[data-theme="dark"] {
+  --color-bg-primary: #111827;
+  --color-bg-secondary: #1f2937;
+  --color-bg-tertiary: #374151;
+  --color-text-primary: #f9fafb;
+  --color-text-secondary: #9ca3af;
+  --color-border-default: #374151;
+}
+
+/* System preference */
+@media (prefers-color-scheme: dark) {
+  :root:not([data-theme="light"]) {
+    --color-bg-primary: #111827;
+    /* ... dark theme values */
+  }
+}
+```
+
+### React Theme Context
+
+```tsx
+import { createContext, useContext, useEffect, useState } from "react";
+
+type Theme = "light" | "dark" | "system";
+
+interface ThemeContextValue {
+  theme: Theme;
+  setTheme: (theme: Theme) => void;
+  resolvedTheme: "light" | "dark";
+}
+
+const ThemeContext = createContext<ThemeContextValue | null>(null);
+
+export function ThemeProvider({ children }: { children: React.ReactNode }) {
+  const [theme, setTheme] = useState<Theme>("system");
+  const [resolvedTheme, setResolvedTheme] = useState<"light" | "dark">("light");
+
+  useEffect(() => {
+    const root = document.documentElement;
+
+    if (theme === "system") {
+      const systemTheme = window.matchMedia("(prefers-color-scheme: dark)")
+        .matches
+        ? "dark"
+        : "light";
+      setResolvedTheme(systemTheme);
+      root.setAttribute("data-theme", systemTheme);
+    } else {
+      setResolvedTheme(theme);
+      root.setAttribute("data-theme", theme);
+    }
+  }, [theme]);
+
+  useEffect(() => {
+    if (theme !== "system") return;
+
+    const mediaQuery = window.matchMedia("(prefers-color-scheme: dark)");
+    const handler = (e: MediaQueryListEvent) => {
+      const newTheme = e.matches ? "dark" : "light";
+      setResolvedTheme(newTheme);
+      document.documentElement.setAttribute("data-theme", newTheme);
+    };
+
+    mediaQuery.addEventListener("change", handler);
+    return () => mediaQuery.removeEventListener("change", handler);
+  }, [theme]);
+
+  return (
+    <ThemeContext.Provider value={{ theme, setTheme, resolvedTheme }}>
+      {children}
+    </ThemeContext.Provider>
+  );
+}
+
+export function useTheme() {
+  const context = useContext(ThemeContext);
+  if (!context) throw new Error("useTheme must be within ThemeProvider");
+  return context;
+}
+```
+
+## Contrast and Accessibility
+
+### WCAG Contrast Checker
+
+```tsx
+function hexToRgb(hex: string): [number, number, number] {
+  const result = /^#?([a-f\d]{2})([a-f\d]{2})([a-f\d]{2})$/i.exec(hex);
+  if (!result) throw new Error("Invalid hex color");
+  return [
+    parseInt(result[1], 16),
+    parseInt(result[2], 16),
+    parseInt(result[3], 16),
+  ];
+}
+
+function getLuminance(r: number, g: number, b: number): number {
+  const [rs, gs, bs] = [r, g, b].map((c) => {
+    c = c / 255;
+    return c <= 0.03928 ? c / 12.92 : Math.pow((c + 0.055) / 1.055, 2.4);
+  });
+  return 0.2126 * rs + 0.7152 * gs + 0.0722 * bs;
+}
+
+function getContrastRatio(hex1: string, hex2: string): number {
+  const [r1, g1, b1] = hexToRgb(hex1);
+  const [r2, g2, b2] = hexToRgb(hex2);
+
+  const l1 = getLuminance(r1, g1, b1);
+  const l2 = getLuminance(r2, g2, b2);
+
+  const lighter = Math.max(l1, l2);
+  const darker = Math.min(l1, l2);
+
+  return (lighter + 0.05) / (darker + 0.05);
+}
+
+function meetsWCAG(
+  foreground: string,
+  background: string,
+  size: "normal" | "large" = "normal",
+  level: "AA" | "AAA" = "AA",
+): boolean {
+  const ratio = getContrastRatio(foreground, background);
+
+  const requirements = {
+    normal: { AA: 4.5, AAA: 7 },
+    large: { AA: 3, AAA: 4.5 },
+  };
+
+  return ratio >= requirements[size][level];
+}
+
+// Usage
+meetsWCAG("#ffffff", "#3b82f6"); // true (4.5:1 for AA normal)
+meetsWCAG("#ffffff", "#60a5fa"); // false (below 4.5:1)
+```
+
+### Accessible Color Pairs
+
+```tsx
+// Generate accessible text color for any background
+function getAccessibleTextColor(backgroundColor: string): string {
+  const [r, g, b] = hexToRgb(backgroundColor);
+  const luminance = getLuminance(r, g, b);
+
+  // Use white text on dark backgrounds, black on light
+  return luminance > 0.179 ? "#111827" : "#ffffff";
+}
+
+// Find the nearest accessible shade
+function findAccessibleShade(
+  textColor: string,
+  backgroundScale: string[],
+  minContrast: number = 4.5,
+): string | null {
+  for (const shade of backgroundScale) {
+    if (getContrastRatio(textColor, shade) >= minContrast) {
+      return shade;
+    }
+  }
+  return null;
+}
+```
+
+## Color Harmony
+
+### Harmony Functions
+
+```tsx
+type HarmonyType =
+  | "complementary"
+  | "triadic"
+  | "analogous"
+  | "split-complementary";
+
+function generateHarmony(baseHue: number, type: HarmonyType): number[] {
+  switch (type) {
+    case "complementary":
+      return [baseHue, (baseHue + 180) % 360];
+    case "triadic":
+      return [baseHue, (baseHue + 120) % 360, (baseHue + 240) % 360];
+    case "analogous":
+      return [(baseHue - 30 + 360) % 360, baseHue, (baseHue + 30) % 360];
+    case "split-complementary":
+      return [baseHue, (baseHue + 150) % 360, (baseHue + 210) % 360];
+    default:
+      return [baseHue];
+  }
+}
+
+// Generate palette from harmony
+function generateHarmoniousPalette(
+  baseHue: number,
+  type: HarmonyType,
+): Record<string, string> {
+  const hues = generateHarmony(baseHue, type);
+  const names = ["primary", "secondary", "tertiary"];
+
+  return Object.fromEntries(
+    hues.map((hue, i) => [names[i] || `color-${i}`, `hsl(${hue}, 70%, 50%)`]),
+  );
+}
+```
+
+## Color Blindness Considerations
+
+```tsx
+// Simulate color blindness
+type ColorBlindnessType = "protanopia" | "deuteranopia" | "tritanopia";
+
+// Matrix transforms for common types
+const colorBlindnessMatrices: Record<ColorBlindnessType, number[][]> = {
+  protanopia: [
+    [0.567, 0.433, 0],
+    [0.558, 0.442, 0],
+    [0, 0.242, 0.758],
+  ],
+  deuteranopia: [
+    [0.625, 0.375, 0],
+    [0.7, 0.3, 0],
+    [0, 0.3, 0.7],
+  ],
+  tritanopia: [
+    [0.95, 0.05, 0],
+    [0, 0.433, 0.567],
+    [0, 0.475, 0.525],
+  ],
+};
+
+// Best practices for color-blind accessibility:
+// 1. Do not rely solely on color to convey information
+// 2. Use patterns or icons alongside color
+// 3. Ensure sufficient contrast between colors
+// 4. Test with color blindness simulators
+// 5. Use blue-orange instead of red-green for contrast
+```
+
+## CSS Color Functions
+
+```css
+/* Modern CSS color functions */
+.modern-colors {
+  /* Relative color syntax */
+  --lighter: hsl(from var(--base-color) h s calc(l + 20%));
+  --darker: hsl(from var(--base-color) h s calc(l - 20%));
+
+  /* Color mixing */
+  --mixed: color-mix(in srgb, var(--color-1), var(--color-2) 30%);
+
+  /* Transparency */
+  --semi-transparent: rgb(from var(--base-color) r g b / 50%);
+
+  /* OKLCH for perceptual uniformity */
+  --vibrant-blue: oklch(60% 0.2 250);
+}
+
+/* Alpha variations */
+.alpha-scale {
+  --color-10: rgb(59 130 246 / 0.1);
+  --color-20: rgb(59 130 246 / 0.2);
+  --color-30: rgb(59 130 246 / 0.3);
+  --color-40: rgb(59 130 246 / 0.4);
+  --color-50: rgb(59 130 246 / 0.5);
+}
+```