Frontend & browser·Accessibility and semantics
the grey-on-white caption looked fine on your monitor and failed the check at 3.1 to 1.
Contrast ratio
Also calledcolour contrast, WCAG contrast
The measured luminance ratio between foreground and background, with WCAG requiring 4.5:1 for normal text, 3:1 for large text and for meaningful non-text elements. It is a computation, not a judgement, which makes it one of the few accessibility criteria that can be enforced automatically. Light grey secondary text and placeholder colours are where nearly every design system fails it.