Measure the foreground and background as a pair, including the real background behind transparent surfaces. Check small text, links, buttons, placeholders, and focus indicators in both light and dark themes if supported.
Use the contrast checker as a numeric starting point, then inspect the design at normal size and brightness. WCAG contrast targets depend on text size and the kind of element; do not apply one threshold blindly to every pixel. Also avoid using color alone to communicate errors or status.
A good color pair remains readable in disabled-looking surroundings and when someone cannot distinguish its hue.
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