SKILL.md
Full skill instructions
OKLCH Colors
OKLCH is a perceptually uniform color space where the numbers actually mean what you think they mean. Most color problems in CSS — broken palettes, failing contrast, hue drift — come from using color spaces that don't match how we see. OKLCH fixes the model so the tools work. To explore interactively, visit oklch.fyi.
Quick Reference
| Category | When to use | Reference |
|---|---|---|
| Conversion | Hex/rgb/hsl to oklch | color-conversion.md |
| Palettes | Generate scales, multi-hue, dark mode | palette-generation.md |
| Contrast | APCA/WCAG checks, fixing failing contrast | accessibility-contrast.md |
| Gamut & Tailwind | P3 fallbacks, @theme scales, gamut clamping | gamut-and-tailwind.md |
Why OKLCH
- Perceptual uniformity. Equal L steps = equal brightness.
oklch(0.5 ...)is visually mid. HSL'slightness: 50%varies wildly by hue. - Stable hue. HSL blue shifts toward purple as lightness changes. OKLCH hue stays constant across the full lightness range.
- Independent chroma. Chroma is an absolute measure of colorfulness that doesn't depend on lightness. HSL saturation does.
- Finite gamut. Not every oklch value maps to a displayable sRGB color. High-chroma values at certain hues will clip — gamut awareness is required.
OKLCH Syntax
oklch(L C H)
oklch(L C H / alpha)
| Channel | Range | Description |
|---|---|---|
| L (Lightness) | 0–1 | 0 = black, 1 = white. Perceptually uniform. |
| C (Chroma) | 0–~0.4 | Colorfulness. 0 = gray. Max depends on L and H. |
| H (Hue) | 0–360 | Hue angle in degrees. |
| alpha | 0–1 | Optional transparency. Slash syntax. |
oklch(0.637 0.237 25.331)
oklch(0.8 0.05 200 / 0.5)
Formatting: L and C use 3 decimal places, H uses up to 3. Drop trailing zeros. Format -0 as 0. Browser support: Baseline 2023, 96%+ global coverage.
Key Thresholds
| Rule | Value |
|---|---|
| Light/dark boundary | L > 0.6 = light background → use dark text |
| Lightness gap (light bg) | Foreground L < 0.45 when background L > 0.85 |
| Lightness gap (dark bg) | Foreground L > 0.75 when background L < 0.25 |
| Hue drift threshold | > 10° spread across palette steps = visible drift |
| APCA normal text | |Lc| >= 60 to pass, >= 75 for pass+ |
| WCAG 2 normal text | 4.5:1 AA, 7:1 AAA |
| Contrast fix | Adjust L only — chroma has negligible effect |
Review Output Format
Always present color changes as a markdown table with Before and After columns. Include every color that was changed — not just a subset. Never list findings as separate "Before:" / "After:" lines outside of a table.
| Before | After |
|---|---|
color: #3b82f6 | color: oklch(0.623 0.188 259.815) |
| Same absolute C across hues | Same C% of each hue's max chroma |
| No sRGB fallback for P3 color | @media (color-gamut: p3) wrapper |
This keeps feedback scannable and diff-friendly. Each row is a self-contained change the developer can act on independently.
Common Mistakes
| Issue | Fix |
|---|---|
| Hex/rgb/hsl color in new code | Convert to oklch() |
| HSL palette ramp with hue drift | Rebuild with constant oklch hue |
| Failing contrast (check foreground vs its background using APCA) | Adjust oklch L channel, keep C and H |
| High chroma without gamut check | Clamp to max chroma for the L/H in sRGB |
| Same absolute C across different hues | Use same C% (percentage of max) for consistent vividness |
| P3 color without sRGB fallback | Add @media (color-gamut: p3) pattern |
| Dark mode with hand-picked colors | Derive from light palette by reversing L mapping |
Hex in Tailwind v4 @theme | Convert to oklch values |
| Alpha with comma syntax | Use slash: oklch(L C H / alpha) |
Reference Files
- color-conversion.md — Supported formats, conversion examples, bulk conversion rules, what to leave alone
- palette-generation.md — Scale convention, generation algorithm, multi-hue palettes, dark mode, why not HSL
- accessibility-contrast.md — APCA and WCAG 2 thresholds, fixing contrast with L, lightness gap guide, hue drift detection
- gamut-and-tailwind.md — sRGB vs P3, gamut clamping, CSS fallback patterns, Tailwind v4 @theme and migration