The difference in luminance between foreground and background colors, critical for text readability and accessibility. WCAG guidelines require minimum contrast ratios of 4.5:1 for normal text and 3:1 for large text. Use contrast checking tools to ensure your color combinations are accessible to users with visual impairments. See Understanding contrast ratio.

Designing and developing websites usable by people with various disabilities including visual, auditory, motor, and cognitive. Accessibility is both ethically important and often legally required. Build accessibility in from the start rather than retrofitting.