colour
APCA
A newer, more perceptually accurate contrast method proposed for WCAG 3 – not yet a standard, and its scores are not compatible with WCAG 2's ratios.
The Accessible Perceptual Contrast Algorithm scores contrast using font size, weight and light/dark polarity together, rather than one flat ratio – fixing real problems with WCAG 2’s maths, which is known to misbehave near the dark end (some near-black-on-black pairs pass 4.5:1 while being genuinely hard to read).
The catch: APCA was pulled from the WCAG 3 working draft in July 2023 after failing to gain consensus, and WCAG 3’s contrast method remains undetermined as of April 2026. WCAG 2.2 is still the only ratio with legal force. If a design passes APCA but fails WCAG 2, shipping it is a legal-risk decision, not a style decision. Sensible 2026 practice: WCAG 2 as the floor, APCA as an optional extra check – never a replacement.