Contrast ratio
Also called: Color contrast
How different text and background colors are; WCAG asks for at least 4.5:1 for normal text.
Definition
Low contrast makes text hard to read, especially in sunlight or for people with low vision. WCAG AA requires 4.5:1 for normal text, 3:1 for large text and for UI parts like icons and input borders. Testers measure it with DevTools or contrast checkers.
In practice
Light grey placeholder text (#BBBBBB) on white has a ratio of about 1.9:1, far below the 4.5:1 minimum.
Learn it in context
Lessons that use this term.