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More about this colour contrast checker:

It’s not true that everyone perceives colours in the same way. Some colour combinations that are easy for you to read may be impossible for someone else, or at least difficult in some cases.

The main reason for our different abilities to perceive colours is due to colour contrast. This is the ability to distinguish between the foreground and background colours’ luminance. Similar colours have a low contrast ratio as compared to a high contrast ratio for vastly different colours.

The WCAG AA guidelines require a minimum contrast ratio of 4.5:1 for all text. The only exception is for very large text for which the ratio can be as low as 3:1. For WCAG Level AAA, the the contrast ratio should be at least 7:1 (or 4.5:1 for large text).

Fun fact: The ratio 4.5:1 compensates for the loss in sensitivity to contrast that is usually experienced by people with a vision loss equivalent to 20/40, which is the typical visual acuity of people at the age of 80.


APCA is the Accessible Perceptual Contrast Algorithm, a new way to predict contrast for text and non-text content on self illuminated displays.


APCA provides a more accurate estimation of human contrast perception than the contrast ratios recommended in WCAG 2.

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