OklchPerceptualUniform [fact] v1.0.0

OKLCH is a perceptually-uniform color space: equal numerical changes in L (lightness) or C (chroma) produce equal perceived changes across all hues. sRGB hex / HSL fail this property — equal HSL lightness deltas read very differently across yellow vs blue.

OKLCH (Björn Ottosson, 2020) is perceptually uniform — a 5-point lightness step in OKLCH looks like the same brightness change regardless of hue, while the equivalent step in HSL produces a much larger change in yellows than in blues — making OKLCH the correct color space for tonal ramps, contrast math, and dark-mode mirroring.

Meta

• License: Apache-2.0
• License Provenance: package-authorship-claim

Confidence

proven

Applies To

• design-token color systems (12-stop ramps)
• dark-mode token derivation (mirror L axis)
• contrast math (predictable APCA / WCAG ratios across hues)
• perceptual gradient interpolation (color-mix in oklch)

Quantitative

• L Axis Range: 0%–100%, perceptually uniform
• C Axis Typical Max: ~0.4 in display-P3, ~0.32 in sRGB
• H Axis Range: 0–360 degrees
• Contrast Deviation From Uniformity: OKLCH < 1% perceptual variance per L step; HSL > 30% across hues

Counter Conditions

• OKLCH's gamut extends beyond sRGB — out-of-gamut OKLCH values get clipped on sRGB displays. Use color-gamut media queries or stay within achievable C for the target gamut.
• OKLCH ≠ Oklab — they are the polar / Cartesian forms of the same space. Browser support for both shipped in 2023.
• Pre-OKLCH alternatives (CIELAB, CIELCh) are also perceptually uniform but produce slightly worse predictions for blue hues — OKLCH improves the blue range specifically.

OklchPerceptualUniform [fact] v1.0.0

OKLCH is a perceptually-uniform color space: equal numerical changes in L (lightness) or C (chroma) produce equal perceived changes across all hues. sRGB hex / HSL fail this property — equal HSL lightness deltas read very differently across yellow vs blue.

OKLCH (Björn Ottosson, 2020) is perceptually uniform — a 5-point lightness step in OKLCH looks like the same brightness change regardless of hue, while the equivalent step in HSL produces a much larger change in yellows than in blues — making OKLCH the correct color space for tonal ramps, contrast math, and dark-mode mirroring.

Meta

• License: Apache-2.0
• License Provenance: package-authorship-claim

Confidence

proven

Applies To

• design-token color systems (12-stop ramps)
• dark-mode token derivation (mirror L axis)
• contrast math (predictable APCA / WCAG ratios across hues)
• perceptual gradient interpolation (color-mix in oklch)

Quantitative

• L Axis Range: 0%–100%, perceptually uniform
• C Axis Typical Max: ~0.4 in display-P3, ~0.32 in sRGB
• H Axis Range: 0–360 degrees
• Contrast Deviation From Uniformity: OKLCH < 1% perceptual variance per L step; HSL > 30% across hues

Counter Conditions

• OKLCH's gamut extends beyond sRGB — out-of-gamut OKLCH values get clipped on sRGB displays. Use color-gamut media queries or stay within achievable C for the target gamut.
• OKLCH ≠ Oklab — they are the polar / Cartesian forms of the same space. Browser support for both shipped in 2023.
• Pre-OKLCH alternatives (CIELAB, CIELCh) are also perceptually uniform but produce slightly worse predictions for blue hues — OKLCH improves the blue range specifically.

Sources

Relations

related: [@community/term-oklch, @community/transform-rgb-to-oklch, @community/constraint-oklch-only-color, @community/fact-contrast-ratio-aa-vs-aaa]

Meta

• License: Apache-2.0
• License Provenance: package-authorship-claim

Confidence

proven

Source

• Björn Ottosson, 'A perceptual color space for image processing' (2020) — bottosson.github.io/posts/oklab/
• CSS Color Module Level 4 — oklch() / oklab() function specification
• Lea Verou, 'LCH colors in CSS: what, why, and how?' (2020)
• Andrew Clark / Evil Martians, 'OKLCH in CSS' explainers (2022–2023)

Applies To

• design-token color systems (12-stop ramps)
• dark-mode token derivation (mirror L axis)
• contrast math (predictable APCA / WCAG ratios across hues)
• perceptual gradient interpolation (color-mix in oklch)

Quantitative

• L Axis Range: 0%–100%, perceptually uniform
• C Axis Typical Max: ~0.4 in display-P3, ~0.32 in sRGB
• H Axis Range: 0–360 degrees
• Contrast Deviation From Uniformity: OKLCH < 1% perceptual variance per L step; HSL > 30% across hues

Counter Conditions

• OKLCH's gamut extends beyond sRGB — out-of-gamut OKLCH values get clipped on sRGB displays. Use color-gamut media queries or stay within achievable C for the target gamut.
• OKLCH ≠ Oklab — they are the polar / Cartesian forms of the same space. Browser support for both shipped in 2023.
• Pre-OKLCH alternatives (CIELAB, CIELCh) are also perceptually uniform but produce slightly worse predictions for blue hues — OKLCH improves the blue range specifically.