The human eye distinguishes between colors based on the difference in how much light they reflect. A ratio of 1:1 means there is no difference, which would be completely invisible text. A ratio of 21:1 is the maximum contrast: black text on a white background. WCAG 2.1 AA, the accessibility standard that most legal guidance references, requires a minimum contrast ratio of 4.5:1 for normal text and 3:1 for large text (defined as fourteen point bold or eighteen point regular). These are minimums, not ideals. Higher contrast is always better for readability.
Insufficient contrast affects more people than most designers realize. Approximately eight percent of men and half a percent of women have some form of color blindness. Many more people have age-related vision changes that reduce contrast sensitivity. Anyone reading in bright sunlight on a mobile device experiences reduced perceived contrast even with eyes that function normally. A design that fails the contrast check for people with typical vision fails even more severely for all of these groups.
The most common contrast failures are predictable: light gray text on a white background, white text on a medium-colored background, colored text on a similar-colored background, and small light text in footer sections. Many of these failures result from aesthetic choices that prioritize a subtle, refined visual palette over readability. The colors that look most sophisticated in a high-quality design environment often fail contrast requirements when tested, particularly at body text sizes.
Testing your color combinations takes less than two minutes. The WebAIM Contrast Checker at webaim.org allows you to enter foreground and background color values and see the resulting ratio and pass-fail status against WCAG AA and AAA standards. Browser extensions like axe DevTools or Colour Contrast Analyser check contrast across your entire live website and flag failures with specific element references. Run these checks on every color combination in your brand palette before finalizing it, and run them again on your live website before launch.
Fixing contrast failures usually means darkening text or lightening or darkening background colors. For brand colors that are near the compliance threshold, a subtle shift in lightness that is invisible to most viewers can be the difference between a passing and failing ratio. Test your adjusted colors in your actual designs after making changes to ensure the aesthetic intention is preserved. In most cases, the adjustment needed to pass is small enough that it does not meaningfully change the visual impression of the design.
Color contrast is one of the simplest accessibility improvements to implement and one of the most directly impactful on how many people can actually read your content, making it the right place to start any accessibility improvement effort.