WCAG

WCAG is the reference document every accessibility law points at. Section 508 in the US, the European Accessibility Act in the EU, AODA in Ontario, and a growing list of national regulations all use WCAG as their legal benchmark. The current version is WCAG 2.2, with WCAG 3 in draft.

WCAG organizes requirements into four principles, known by the POUR acronym: Perceivable, Operable, Understandable, Robust. Each principle breaks down into specific success criteria with levels A, AA, and AAA. AA is the standard most commercial products aim for. AAA is reserved for specialized contexts where failure has legal or safety consequences.

For color, WCAG defines three thresholds: 4.5:1 for body text, 3:1 for large text, and 3:1 for non-text UI elements (buttons, form borders, focus rings, meaningful icons). The ratios are legally enforceable in most jurisdictions. They are also computed from a formula that is widely acknowledged to be perceptually inaccurate, which is why APCA is being proposed as the replacement in WCAG 3.

The practical move is to meet WCAG 2 AA for compliance and supplement with APCA or perceptual testing for actual quality. A page can pass WCAG 2 and still be hard to read. A page that hits both WCAG 2 AA and APCA thresholds is readable by design.