Usability and Accessibility

Excellent feedback from a Ryan O’Malley today on the Callisti fledgling website: the colour contrast between text and background is not properly readable!

“The W3C recommends a standard of 500 or greater for the color difference and a standard of 125 or greater for color brightness” and more information is at the Colour Contrast Analyser resource.

In fact the Colour brightness formula goes like this:

To conform with Web Content Accessibility Guidelines 1.0, foreground and background color combinations should provide sufficient contrast when viewed by someone with low vision or colour blindness, or when viewed on a black and white screen.

The formula suggested by the World Wide Web Consortium (W3C) to determine the brightness of a colour is:

((Red value X 299) + (Green value X 587) + (Blue value X 114)) / 1000

Two colours provide good colour visibility if the brightness difference is greater then 125 and the color difference is greater then 500.

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