Contrast and distinctness

Check foreground contrast and separation between related colors.

Core principles

  • Check contrast and state separation independently.
  • Identify important states with text or symbols as well as color.

Model

  • The Accessible Perceptual Contrast Algorithm (APCA) accounts for contrast polarity.
  • Distinctness analysis compares perceptual color distance and color-vision simulations.

Use in your app

  • Check semantic foreground and background pairs in both color modes.
  • Inspect warning, selected, disabled, and placeholder states.

Verification scope

  • Fixtures report failures for declared contrast and distinctness limits. Passing calculations do not certify accessibility.

Token notes

  • Each fixture identifies the token pairs and conditions it evaluates.