Do not round contrast before checking a threshold

Contrast is calculated from the relative luminance of two colors. Black against white gives 21:1; identical colors give 1:1. Different hues alone do not make text readable.

This tool evaluates two opaque RGB colors using WCAG contrast calculations. Display rounding does not affect the underlying pass/fail check. An actual ratio of 4.49 does not meet a 4.5 threshold even if rounded display text appears to say 4.5.

With transparency, photographs or gradients, inspect the composited color directly behind the text. A contrast check alone cannot establish accessibility of the whole page.