Use of Color

What it asks

Whenever the meaning of a UI element depends on its color — a red error message, a green “available” dot, a blue link inside body text, a colored line on a chart — that meaning must also be conveyed by something other than color. The SC does not ban color, it bans color-only. Roughly 1 in 12 men and 1 in 200 women have some form of color-vision deficiency; on top of that, monochrome printouts, dim screens, and high-glare environments routinely erase color distinctions.

How to meet it

• Underline links inside paragraphs of text. A different color alone fails — it’s the canonical 1.4.1 failure.
• Pair every status color with a label or icon: red with “Error” text, green with a checkmark, yellow with a warning triangle.
• Mark required form fields with both color (asterisk in red) and a textual indicator (“required”).
• For charts, use distinct line styles (solid, dashed, dotted) or symbols at data points, not just color.
• Map “available / busy / away” status indicators to color plus icon shape (filled circle, hollow circle, dash).
• For form validation, the invalid state must have an error message in addition to a red border.

Common failures

• Links in body text shown only by a slightly different blue with no underline. Red-green color-blind users see no distinction.
• Required-field asterisks shown in red with no aria-required and no “required” label.
• Charts with five series differentiated only by color — print the chart in grayscale and the lines become indistinguishable.
• Error states styled with a red border only, no error message text.
• “Online / offline” indicators that change only color, no shape or label change.
• Pie charts with similar-luminance slices labelled only in the legend by color.

Why it matters

This is the most-cited 1.4.x failure and one of the easiest to fix at design time — add an underline, add an icon, add a label. Retrofitting is harder because the brand palette is often built around color-only signaling. The QualiBooth / axe / Lighthouse rules can’t always detect this automatically, so it surfaces in manual review.