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Colour Blindness

Colour blindness, as a form of visual impairment, is often forgotten.  For many people it does not cause significant difficulties in their everyday life.  If, however, an individual relies on the interpretation of colour as part of their work (e.g. interpretation of maps, charts, diagrams etc.) this can lead to significant problems if the information is not presented in a way that they can interpret.

What is colour blindness and how does it affect people?

Colour blindness is usually transmitted genetically, but can also be caused by brain, eye or nerve damage. There are three commonly occurring types of colour blindness:

  • total colour blindness
  • red-green colour blindness
  • blue-yellow colour blindness.

People without colour blindness can see colours in daylight through the cone cells in the eye. Different colours of light are signalled to the brain by three different types of cones: absorbing short wavelengths (blue colours), medium wavelengths (green colours) or long wavelengths (red colours).

The rainbow flag below illustrates how different people view colours depending on their vision.

No colour blindness

Rainbow flag




Defect red cones (orange and green appear as the same colour)

Rainbow flag but with orange and green shown as the same colour)




Defect green cones (red and green appear as the same colour)

Rainbow flag with red and green shown as the same colour




Defect blue cones

Rainbow flag with blue tones

How to make your material accessible

  1. Think about how other people might see your information. You can use an online colour blind simulation tool to test how colour-blind people might see your information.
  2. Avoid using red and green in the same image to illustrate important information, or check whether the information you want to show is hidden from colour-blind people e.g. using one of the links above.
  3. Use high contrast to highlight important features in your image.
  4. When it is not possible to improve the visibility of the information in diagrams, tables and other illustrations, aim to include sufficient narrative to describe the points being illustrated.
  5. Avoid conveying meaning in images where the meaning is not also repeated in the text