The Web Content Accessibility Guidelines define three conformance levels: A (minimum accessibility), AA (the widely accepted standard), and AAA (enhanced accessibility). For color, the differences are significant and directly affect which color combinations you can use.
Level A: The Bare Minimum
Level A for color primarily requires SC 1.4.1: information must not be conveyed by color alone. This means every color-coded element (red errors, green success, colored charts) must also use text, icons, or other non-color indicators. Level A has no contrast ratio requirements for text.
Level AA: The Standard Target
Level AA adds contrast requirements: 4.5:1 for normal text (SC 1.4.3), 3:1 for large text, and 3:1 for UI components and graphical objects (SC 1.4.11). WCAG 2.2 adds focus indicator requirements (SC 2.4.11, 2.4.12, 2.4.13) that have color implications. AA is the legal standard in many jurisdictions and the target for most organizations.
Level AAA: The Gold Standard
Level AAA increases the text contrast requirement to 7:1 for normal text and 4.5:1 for large text (SC 1.4.6). This significantly narrows the usable color combinations but provides the best experience for users with low vision. AAA is rarely required legally but is achievable for color and worth pursuing.
What This Means for Your Palette
Targeting AA means your body text needs 4.5:1 contrast against its background. This allows medium-dark text on light backgrounds or light text on dark backgrounds. Targeting AAA (7:1) requires either very dark text on light backgrounds or very light text on dark backgrounds, with less room for medium tones.
PaletteRx's Approach
PaletteRx's Step 3 contrast grid shows both AA and AAA pass/fail status for every pair. This lets you quickly see which pairs pass only AA versus which also pass AAA, allowing you to make informed decisions about where to use each combination.