color-palette

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npx skills add jezweb/claude-skills --skill color-palette

Documentation

SKILL.md

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Documentation

SKILL.md

Colour Palette Generator

Generate a complete, accessible colour system from a single brand hex. Produces Tailwind v4 CSS ready to paste into your project.

Workflow

Step 1: Get the Brand Hex

Ask for the primary brand colour. A single hex like #0D9488 is enough.

Step 2: Generate 11-Shade Scale

Convert hex to HSL, then generate shades by varying lightness while keeping hue constant.

Hex to HSL Conversion

function hexToHSL(hex) {
  hex = hex.replace(/^#/, '');
  const r = parseInt(hex.substring(0, 2), 16) / 255;
  const g = parseInt(hex.substring(2, 4), 16) / 255;
  const b = parseInt(hex.substring(4, 6), 16) / 255;
 
  const max = Math.max(r, g, b);
  const min = Math.min(r, g, b);
  const diff = max - min;
 
  let l = (max + min) / 2;
  let s = 0;
  if (diff !== 0) {
    s = l > 0.5 ? diff / (2 - max - min) : diff / (max + min);
  }
 
  let h = 0;
  if (diff !== 0) {
    if (max === r) h = ((g - b) / diff + (g < b ? 6 : 0)) / 6;
    else if (max === g) h = ((b - r) / diff + 2) / 6;
    else h = ((r - g) / diff + 4) / 6;
  }
 
  return { h: Math.round(h * 360), s: Math.round(s * 100), l: Math.round(l * 100) };
}

Lightness and Saturation Values

Shade	Lightness	Saturation Mult	Use Case
50	97%	0.80	Subtle backgrounds
100	94%	0.80	Hover states
200	87%	0.85	Borders, dividers
300	75%	0.90	Disabled states
400	62%	0.95	Placeholder text
500	48%	1.00	Brand colour baseline
600	40%	1.00	Primary actions (often the brand colour)
700	33%	1.00	Hover on primary
800	27%	1.00	Active states
900	20%	1.00	Text on light bg
950	10%	1.00	Darkest accents

Reduce saturation for lighter shades (50-200 by 15-20%, 300-400 by 5-10%) to prevent overly vibrant pastels. Keep full saturation for 500-950.

Complete Scale Generator

function generateShadeScale(brandHex) {
  const { h, s } = hexToHSL(brandHex);
  const shades = {
    50:  { l: 97, sMul: 0.8 },  100: { l: 94, sMul: 0.8 },
    200: { l: 87, sMul: 0.85 }, 300: { l: 75, sMul: 0.9 },
    400: { l: 62, sMul: 0.95 }, 500: { l: 48, sMul: 1.0 },
    600: { l: 40, sMul: 1.0 },  700: { l: 33, sMul: 1.0 },
    800: { l: 27, sMul: 1.0 },  900: { l: 20, sMul: 1.0 },
    950: { l: 10, sMul: 1.0 }
  };
  const result = {};
  for (const [shade, { l, sMul }] of Object.entries(shades)) {
    result[shade] = `hsl(${h}, ${Math.round(s * sMul)}%, ${l}%)`;
  }
  return result;
}

HSL to Hex Conversion

function hslToHex(h, s, l) {
  s = s / 100; l = l / 100;
  const c = (1 - Math.abs(2 * l - 1)) * s;
  const x = c * (1 - Math.abs((h / 60) % 2 - 1));
  const m = l - c / 2;
  let r = 0, g = 0, b = 0;
  if (h < 60) { r = c; g = x; }
  else if (h < 120) { r = x; g = c; }
  else if (h < 180) { g = c; b = x; }
  else if (h < 240) { g = x; b = c; }
  else if (h < 300) { r = x; b = c; }
  else { r = c; b = x; }
  r = Math.round((r + m) * 255);
  g = Math.round((g + m) * 255);
  b = Math.round((b + m) * 255);
  return `#${r.toString(16).padStart(2, '0')}${g.toString(16).padStart(2, '0')}${b.toString(16).padStart(2, '0')}`.toUpperCase();
}

Verification

Generated shades should look like the same colour family with smooth progression. Light shades (50-300) usable for backgrounds, dark shades (700-950) usable for text. Brand colour recognisable in 500-700.

Step 3: Map Semantic Tokens

Every background token MUST have a paired foreground token. Never use a background without its pair or dark mode will break.

Light Mode Tokens

Token	Shade	Use Case
`background`	white	Page backgrounds
`foreground`	950	Body text
`card`	white	Card backgrounds
`card-foreground`	900	Card text
`popover`	white	Dropdown/tooltip backgrounds
`popover-foreground`	950	Dropdown text
`primary`	600	Primary buttons, links
`primary-foreground`	white	Text on primary buttons
`secondary`	100	Secondary buttons
`secondary-foreground`	900	Text on secondary buttons
`muted`	50	Disabled backgrounds, subtle sections
`muted-foreground`	600	Muted text, captions
`accent`	100	Hover states, subtle highlights
`accent-foreground`	900	Text on accent backgrounds
`destructive`	red-600	Delete buttons, errors
`destructive-foreground`	white	Text on destructive buttons
`border`	200	Input borders, dividers
`input`	200	Input field borders
`ring`	600	Focus rings

Dark Mode Tokens

Token	Shade	Use Case
`background`	950	Page backgrounds
`foreground`	50	Body text
`card`	900	Card backgrounds
`card-foreground`	50	Card text
`popover`	900	Dropdown backgrounds
`popover-foreground`	50	Dropdown text
`primary`	500	Primary buttons (brighter in dark)
`primary-foreground`	white	Text on primary buttons
`secondary`	800	Secondary buttons
`secondary-foreground`	50	Text on secondary buttons
`muted`	800	Disabled backgrounds
`muted-foreground`	400	Muted text
`accent`	800	Hover states
`accent-foreground`	50	Text on accent backgrounds
`destructive`	red-500	Delete buttons (brighter)
`destructive-foreground`	white	Text on destructive
`border`	800	Borders
`input`	800	Input borders
`ring`	500	Focus rings

Dark Mode Inversion Pattern

Dark mode inverts lightness while preserving hue and saturation. Swap extremes (50 becomes 950, 950 becomes 50), preserve middle (500 stays near 500).

Light Shade	Dark Equivalent	Role
50	950	Backgrounds
100	900	Subtle backgrounds
200	800	Borders
500	500 (slightly brighter)	Brand baseline
600	400	Primary actions
950	50	Text colour

Key dark mode principles:

Use shade 500 (not 600) for primary -- brighter for visibility on dark backgrounds
Use shade 50 (off-white) for text instead of pure #FFFFFF -- easier on eyes
Borders need ~10-15% lighter than background (e.g. 800 border on 950 background)
Higher elevation = lighter colour (opposite of light mode shadows)
Always update foreground when changing background

Step 4: Check Contrast

WCAG Minimum Ratios

Content Type	AA	AAA
Normal text (<18px or <14px bold)	4.5:1	7:1
Large text (>=18px or >=14px bold)	3:1	4.5:1
UI components (buttons, borders)	3:1	Not defined
Graphical objects (icons, charts)	3:1	Not defined

Target AA for most projects, AAA for high-accessibility needs (government, healthcare).

Luminance and Contrast Formulas

function getLuminance(hex) {
  hex = hex.replace(/^#/, '');
  const r = parseInt(hex.substring(0, 2), 16) / 255;
  const g = parseInt(hex.substring(2, 4), 16) / 255;
  const b = parseInt(hex.substring(4, 6), 16) / 255;
  const rsRGB = r <= 0.03928 ? r / 12.92 : Math.pow((r + 0.055) / 1.055, 2.4);
  const gsRGB = g <= 0.03928 ? g / 12.92 : Math.pow((g + 0.055) / 1.055, 2.4);
  const bsRGB = b <= 0.03928 ? b / 12.92 : Math.pow((b + 0.055) / 1.055, 2.4);
  return 0.2126 * rsRGB + 0.7152 * gsRGB + 0.0722 * bsRGB;
}
 
function getContrastRatio(hex1, hex2) {
  const lum1 = getLuminance(hex1);
  const lum2 = getLuminance(hex2);
  const lighter = Math.max(lum1, lum2);
  const darker = Math.min(lum1, lum2);
  return (lighter + 0.05) / (darker + 0.05);
}

Quick Check Table -- Light Mode

Foreground	Background	Ratio	Pass?	Use Case
950	white	18.5:1	AAA	Body text
900	white	14.2:1	AAA	Card text
700	white	8.1:1	AAA	Text
600	white	5.7:1	AA	Text, buttons
500	white	3.9:1	Fail	Too light for text
white	600	5.7:1	AA	Button text
white	700	8.1:1	AAA	Button text
600	50	5.4:1	AA	Muted section text

Quick Check Table -- Dark Mode

Foreground	Background	Ratio	Pass?	Use Case
50	950	18.5:1	AAA	Body text
50	900	14.2:1	AAA	Card text
400	950	8.2:1	AAA	Muted text
400	900	6.3:1	AA	Muted text
white	600	5.7:1	AA	Button text

Rule of thumb: For text, aim for 50%+ lightness difference between foreground and background.

Essential Pairs to Verify

Body text: foreground on background (light: 950 on white = 18.5:1, dark: 50 on 950 = 18.5:1)
Primary button: primary-foreground on primary (light: white on 600 = 5.7:1, dark: white on 500 = 3.9:1 -- borderline)
Muted text: muted-foreground on muted (light: 600 on 50 = 5.4:1, dark: 400 on 800 = 4.1:1 -- may fail)
Card text: card-foreground on card (light: 900 on white = 14.2:1, dark: 50 on 900 = 14.2:1)

Fixing Common Contrast Failures

White on primary-500 fails (3.9:1): Use primary-600 instead (5.7:1), or use dark text on the button.

Muted text in dark mode fails (400 on 800 = 4.1:1): Use 300 on 900 = 6.8:1.

Links hard to see (500 on white = 3.9:1): Use primary-700 (8.1:1), or add underline decoration.

Step 5: Output Tailwind v4 CSS

@import "tailwindcss";
 
@theme {
  /* Shade scale */
  --color-primary-50: #F0FDFA;
  --color-primary-100: #CCFBF1;
  --color-primary-200: #99F6E4;
  --color-primary-300: #5EEAD4;
  --color-primary-400: #2DD4BF;
  --color-primary-500: #14B8A6;
  --color-primary-600: #0D9488;
  --color-primary-700: #0F766E;
  --color-primary-800: #115E59;
  --color-primary-900: #134E4A;
  --color-primary-950: #042F2E;
 
  /* Light mode semantic tokens */
  --color-background: #FFFFFF;
  --color-foreground: var(--color-primary-950);
  --color-card: #FFFFFF;
  --color-card-foreground: var(--color-primary-900);
  --color-popover: #FFFFFF;
  --color-popover-foreground: var(--color-primary-950);
  --color-primary: var(--color-primary-600);
  --color-primary-foreground: #FFFFFF;
  --color-secondary: var(--color-primary-100);
  --color-secondary-foreground: var(--color-primary-900);
  --color-muted: var(--color-primary-50);
  --color-muted-foreground: var(--color-primary-600);
  --color-accent: var(--color-primary-100);
  --color-accent-foreground: var(--color-primary-900);
  --color-destructive: #DC2626;
  --color-destructive-foreground: #FFFFFF;
  --color-border: var(--color-primary-200);
  --color-input: var(--color-primary-200);
  --color-ring: var(--color-primary-600);
  --radius: 0.5rem;
}
 
/* Dark mode overrides */
.dark {
  --color-background: var(--color-primary-950);
  --color-foreground: var(--color-primary-50);
  --color-card: var(--color-primary-900);
  --color-card-foreground: var(--color-primary-50);
  --color-popover: var(--color-primary-900);
  --color-popover-foreground: var(--color-primary-50);
  --color-primary: var(--color-primary-500);
  --color-primary-foreground: #FFFFFF;
  --color-secondary: var(--color-primary-800);
  --color-secondary-foreground: var(--color-primary-50);
  --color-muted: var(--color-primary-800);
  --color-muted-foreground: var(--color-primary-400);
  --color-accent: var(--color-primary-800);
  --color-accent-foreground: var(--color-primary-50);
  --color-destructive: #EF4444;
  --color-destructive-foreground: #FFFFFF;
  --color-border: var(--color-primary-800);
  --color-input: var(--color-primary-800);
  --color-ring: var(--color-primary-500);
}

Copy assets/tailwind-colors.css as a starting template.

Component Usage Examples

// Primary button
<button className="bg-primary text-primary-foreground hover:bg-primary/90">Click me</button>
 
// Secondary button
<button className="bg-secondary text-secondary-foreground hover:bg-secondary/80">Cancel</button>
 
// Card
<div className="bg-card text-card-foreground border-border rounded-lg">
  <h2>Title</h2>
  <p className="text-muted-foreground">Description</p>
</div>
 
// Input
<input className="bg-background text-foreground border-input focus:ring-ring" />

Common Adjustments

Too vibrant at light shades: Reduce saturation by 10-20%
Poor contrast on primary: Use shade 700+ for text
Dark mode too dark: Use shade 900 instead of 950 for backgrounds
Brand colour too light/dark: Adjust to shade 500-600 range
Dark mode looks washed out: Use shade 500 for primary (brighter than light mode's 600)
Pure white text too harsh in dark mode: Use shade 50 (off-white) instead
Dark mode muted text fails contrast: Use more extreme shades (300 on 900 instead of 400 on 800)

Brand Identity Adjustments

Conservative brands (finance, law): Use primary-700 for buttons, reduce saturation in light shades
Vibrant brands (creative, tech): Use primary-500-600, keep full saturation
Minimal brands (design, architecture): Use primary sparingly, emphasise muted tones, subtle borders (primary-100)

Verification Checklist

Test both modes before shipping.

Optional References

Online contrast checkers: WebAIM (webaim.org/resources/contrastchecker), Coolors (coolors.co/contrast-checker), Accessible Colors (accessible-colors.com)
CI/CD contrast tests: Use getContrastRatio() in test suites to assert minimum ratios for all token pairs
Transparent/gradient edge cases: For colours with opacity, calculate against final rendered colour. For gradients, check both endpoints.
OLED dark mode: Use @media (prefers-contrast: high) with #000000 background for battery savings on AMOLED screens
Multi-colour palettes: Generate separate shade scales for each brand colour, map to different semantic roles (primary, accent)
Palette visualisation tools: coolors.co, paletton.com, Figma swatches
assets/tailwind-colors.css — Complete CSS output template