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Can you tell red from green?

By Dr Alex Wade, Research Fellow at Stanford University

(this article appeared in Planet Medica, April 2000)

The next time you go strawberry picking, imagine how much harder it would be if the fruit were the same colour as the leaves. If you are a man, there is a 10% chance that they are! So is this a problem you need to worry about?

photo of mock strawberry plants* color-deficient simulation of mock strawberry plants

Mock strawberries*.

Mock strawberries as they would appear to someone who is red/green colorblind.

Roughly 1 in 10 men are fully or partly colour blind. This means that one of the three types of colour detectors in their eyes is either faulty or missing altogether.The condition is hereditary and sex-linked: fathers will pass the gene to their daughters (but not their sons) andmothers can pass it to all their children. However, because women can be unaffected carriers, men are at least 20 times more likely than women to develop colour blindness.

Colour blindness is not a particularly serious condition. Although one type of colour detector (or cone cell) is missing, the gaps are filled seamlessly by cones of the other two sorts. The more important aspects of vision are rarely affected. People who are colour blind are, in general, no more likely to suffer from short- or long-sightedness or to develop eye diseases such as glaucoma or cataracts later in life.

The effects of colour blindness are so mild that many boys only realise that they have it at a relatively late age. Since they were born colour blind, the world has always looked perfectly normal to them. It is only when they have a sight test at school, or get into an argument with a friend about whether something is red or green, that they find their view of the world does not always match that of other people.

It is important to remember that people with colour blindness generally can see most colours; they just have trouble distinguishing between some shades of red and green. Apart from making terrible strawberry pickers, people who are colour blind are excluded from certain jobs for safety reasons. For example, they cannot be airline pilots, policemen or ship captains. Their everyday lives are also fraught with occasional minor hazards: how to match socks, how to decide whether the power indicator on the stereo is red or green, how to find red golf tees in the grass and how to choose an appropriate colour scheme for decorating the house.

Clever ways to compensate for colour blindness

If you are colour blind, there are some strategies that can help. Getting a friend or partner to advise on matching socks and ties will stop you committing the more serious fashion crimes, while asking a shop assistan's advice when buying clothes, paint, carpets and wallpaper is just common sense. Most colour-blind people learn at an early age to use clues to help them guess what colour something might be. Red and green traffic lights might look similar, but knowing that red is always at the top can help (although see footnote below). Often, red and green things that look alike under fluorescent light will look different in the daylight. Try taking your ties nearer to the window in a shop before you decide which one to buy.

On the positive side, there is some evidence that colour-blind people are much better than average at certain jobs. They are very good at finding green things hidden against green backgrounds - for example grass or leaves. They tend to find things by shape and get less confused by camouflage. Because of this, colour-blind entomologists still catch lots of bugs and in wartime, armies prize their colour-blind snipers and spotters. So, if you are colour blind and have trouble picking strawberries, why not try your hand at green beans or peas instead? You might be surprised at how well you do!


One of our readers took issue with the traffic light idea:

I found your site very interesting. However I would like to disagree with you regarding your example of the red traffic light. The spectrum of the red light is predominantly red and being moderatly colourblind for red I find the intensity of the red light diminished. If I am a distance away from the light the amplitude of light is to low for me to see at all and thus can't determine if it is the top, middle or bottom light burning. There just are no light! As I get closer to the light the intensity increases and I start to see the red light. To compensate I watch the other vehicles ahead and on my side and if they start to reduce speed I know there must be a red light ahead. Bear in mind that light intensity decreases by the square of the distance. That is if you double the distance from the light source you only get a quarter of the light.

* Thanks to Roman Molas for pointing out that these are mock strawberries

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