I am colourblind, as is around 10% of men and 0.5% of women. Now, before I talk about how this affects computers, let me first explain what colourblindness is and isn’t for the uninitiated.

A normal-sighted person sees colours as they are using 3 different colour receptors in the eye, detecting red, blue and green light respectively. The eye also has receptors which see in shades of grey, which is used in low light levels (which is why you lose colour vision when it is dark).

Do you see a number 74 in here?

Do you see a number 74 in here?

Many people aren’t aware that colourblindness comes in several different forms and severity, the most common being red-green colourblindness, where the person sees red and green as the same colour. Colourblindness occurs when one or more of the colour receptors does not work as it should, or does not function at all. So for example, in red-green colourblindness, the red and green receptors incorrectly react to the same frequencies of light, or you may find that the receptor does not work at all, in which case that colour will appear black.

Now how does this affect computers? Well, for one thing, often green is used to indicate that all is ok, and red that an error occurred. A red-green colourblind person would not notice a difference. I was just reading that in games too the enemies are often tagged in red and the good guys in green – so then who do you shoot?

A more subtle problem is when the programmer or web designer themselves is colourblind. For example, it is a rather bad idea to trust my opinion on colour. I have a blue-green colourblindness which means that my colours would probably appear slightly off to a normal sighted person. I once painted our bathroom an avocado green colour because I thought it looked nice, much to the horror of my family who thought I had gone mad.

Implied in the problem about choosing colours for computer applications and webpages is also the problem of sites and applications that look great for a normal sighted person, but become useless for a colourblind person. It is often a good idea to either let the colours be configurable or else choose safe colours.

And before I end, a little interesting fact – most colourblind people will not realise they see the world differently until it is pointed out to them. For us, the world just looks normal.