oklch-skill

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's lightness: 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