ColorContrast.App

Color contrast checker is a online tool to check the contrast and accessibility of different color combinations based on WCAG or APCA standards.

You can also simulate various forms of color blindness.

How does the color contrast checker work? The Polypane color contrast checker checks against values defined by the WCAG 2 (Web Content Accessibility Guidelines) or APCA (the Accessible Perceptual Contrast Algorithm). WCAG give a formula to calculate the contrast, ranging from 1 (no contrast) to 21 (black on white). APCA has a range from minus ~106 to plus ~106.

The Polypane contrast checker takes opacity into account when calculating the colors, giving you the real contrast ratio.

How are the suggested colors calculated? When the contrast is not sufficient, we'll suggest you similar colors that do have enough contrast. We do this by increasing or decreasing the luminance of the foreground color until it has enough contrast. When the foreground color can not be changed (because it's too close to full black or full white) we will suggest an accessible background color instead.