Contrast ratio
A number from 1:1 to 21:1 that compares the brightness of two colors, used to check text is readable.
Also called color contrast, contrast
The contrast ratio compares the relative luminance of two colors. White on black is 21:1, the maximum; the same color on itself is 1:1.
WCAG asks for at least 4.5:1 for normal text and 3:1 for large text. Every color page on Swatch.ing shows its contrast against white and black.
Guides that cover Contrast ratio
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