What is color contrast ratio?

Contrast ratio is one of the few accessibility requirements that is purely arithmetic: luminance values are computed from the two colours and compared, producing a figure between 1:1 and 21:1. WCAG sets thresholds by text size and purpose, and the calculation admits no interpretation — a colour pair either meets the threshold or does not. This makes it the most automatable accessibility check and, in practice, one of the most commonly failed, because brand palettes are chosen for appearance and applied to text without the ratio ever being computed. Centralpoint treats accessibility as a governed property rather than a design preference, so contrast conformance is measurable across published content rather than assessed page by page. Where a design system is applied consistently, a single palette correction resolves the failure across the estate rather than requiring individual remediation.