WCAG 2.2 vs APCA: Where Contrast Standards Are Headed
Text contrast has a standard you need to meet now, and a newer model that's getting a lot of attention. They're easy to confuse, and the difference matters legally. Here's the honest state of things.
WCAG is today's standard
WCAG Level AA requires a contrast ratio of at least 4.5:1 for normal text, and 3:1 for large text and UI components — the same thresholds in 2.0, 2.1, and 2.2. WCAG is the accessibility baseline cited by laws and procurement standards worldwide, though each pins a specific version: the ADA Title II rule and the EU's EN 301 549 reference 2.1 AA, US Section 508 references 2.0 AA, and 2.2 is the newest W3C Recommendation. The AA contrast criteria are unchanged across these versions, so meeting 2.2 AA satisfies the 2.1 and 2.0 contrast requirements too. If you need to be compliant, that's the bar — meet it.
What APCA tries to improve
WCAG's simple ratio is known to misjudge some pairs — particularly light text and dark-mode combinations — sometimes passing things that look poor or failing things that look fine. APCA (the Accessible Perceptual Contrast Algorithm) models perceived contrast more faithfully, reporting a signed lightness contrast (Lc) instead of a ratio.
But APCA is experimental. It is proposed for WCAG 3, which is an early Working Draft — and that draft does not currently name APCA. So APCA is not normative and not a requirement. Treat it as a refined second opinion, never as a standard you can claim to 'pass' for compliance.
How to use both
Design to WCAG 2.2 AA — it's the newest version, and meeting it also satisfies the 2.1 and 2.0 AA baselines that laws actually cite — and use APCA as a sanity check when the ratio feels off, especially in dark mode or with thin type. Report them as what they are: WCAG as the standard, APCA as experimental guidance.
Contrast alone isn't enough
Passing a contrast check doesn't make an interface accessible. Don't rely on color by itself to convey meaning — link styling, form states, and chart series all need a non-color cue (text, an icon, an underline, a pattern) so people who can't distinguish the colors aren't shut out.