Seeing Red – or is it Green?

Colour diagram showing the three different types of colour vision deficiencyNot everyone experiences colour in the same way, yet the use of colour in illustrations is rarely questioned in terms of universal design. If people with Colour Vision Deficiency (CVD) are not included when illustrations, charts and images are designed, what colours should a designer use to include the 8% of the population with CVD? There are three types of CVD as shown in the image: green blindness, blue blindness and red blindness. People with CVD also have other difficulties in discerning some types of text, shapes and lines.

Preparing Images for All to See explains in detail how people with different versions of CVD experience colour. The article also gives some great guidelines for illustrators, map makers and others who communicate using coloured images. Included is a summary of the most frequently cited best practices for publication, presentation and instruction. Here is a synopsis of their recommendations.

  1. Select graphic styles for accessibility and use bar charts instead of pie charts 
  2. Distinguish items by more than color. Use circles and squares and solid and dashed lines. 
  3. Red and Green usually have the same hue (density of colour) and can’t be distinguished. Dark red–dark green, blue–violet, red–orange, and yellow–green are also not good. Magenta and turquoise are good choices because people with RedGreen-CVD can see the blue component.
  4. Make fonts and lines thick bright and with contrast.  
  5. Avoid rainbow color maps as this is the worst possible choice

You can also find out more about CVD or colour blindness from going to the National Eye Institute website

Three circular charts showing how people with colour deficiency see different colours on the colour wheel