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Use of colour: Colour blindness

With regard to colour blind visitors, it is important that web developers pay enough attention to the use of colour on web pages. Apart from the meaning of information on a web page, the readability of that information is another point to consider.

A few rules of thumb for use of colour for colour blind visitors

It is better to avoid the following colour combinations.

  • Green, red, orange, brown and yellow
  • Purple and blue
  • Red on black or black on red, or adjacent to one another.
  • Pastels

Exceptions

  • If the abovementioned colour combinations are used as a background with a white text on top of it, providing sufficient grey contrast.
  • If boxes of the abovementioned colours are used side by side (for navigation buttons for example), where these boxes can be distinguished from each other (for instance, separated by white space)
  • If there is sufficient difference in brightness (for instance, a pale yellow text on a dark green button).

Greyscale testing

Most computers include accessibility options for users who are visually impaired. These options can be used by web developers to run tests. A monitor set to greyscale will give an impression of colour accessibility for people with normal vision, people with impaired vision and colour blind viewers. Web developers can use this tool for checking the contrast in colour brightness. Many computers contain accessibility options which developers can use for testing.


Web Guidelines version 1.3, November 2007.