Colour blindness

Types of colour blindness

The most common type of colour blindness is red–green colour blindness. This affects around 1 in 12 men and around 1 in 200 women. ¹,² If you have this type of colour blindness, you will have difficulty distinguishing between red, yellow and green. You may also confuse red with black or have difficulty distinguishing different shades of purple from blue.

Types of colour blindness can also be classified based on which cones are damaged or missing. If the cones for detecting red light are missing or don’t work properly, this is called protanopia or protan colour blindness. If the cones for detecting green light are missing or don’t work properly, this is called deuteranopia or deutan colour blindness. Protanopia and deuteranopia both result in red–green colour blindness (because if you can’t see red or you can’t see green, then you can’t distinguish between red and green).

If the cones for detecting blue light are missing or don’t work properly, this is called tritanopia. This means you cannot see blue, so you will be blue-yellow colour blind. This is sometimes incorrectly described as being blue–green colour blind.

Blue–yellow colour blindness is less common than red–green colour blindness. It affects less than 1% of both men and women.² Blue–yellow colour blindness makes it difficult to distinguish between blue and green, and also between yellow and red. Shades of blue look green or even black. Yellow looks white, orange looks pink, and purple looks red.

Finally, if two types or all three types of cones are missing or damaged, you will not be able to distinguish between colours at all. It is very rare to be completely unable to distinguish any colours. This condition is called achromatopsia or monochromacy. If you have total colour blindness, you will see everything in shades of grey.

Testing for colour blindness

There are simple tests your optometrist can give you to see if you are colour blind.

The main colour blindness test is called the Ishihara colour test. This involves a circle filled with different coloured spots. There is a number “hidden” in the spots, in different colours. For example, there could be a number 3 traced out in different shades of green spots, against a background of different shades of red spots. If you aren’t colour blind, you’d easily be able to see the green ‘3’ against the red background. However, if you have red-green colour blindness, you would just see a lot of spots with no obvious pattern to them.

There are different versions of the test with different foreground and background colours, which check for different types of colour blindness.

For very young children who cannot read numbers yet, the test can be done using simple shapes instead, or by asking them to trace a path across the circle of spots.

There are basic screening checks for colour blindness which can be done online. However, if you suspect that you or your child are colour blind based on a colour vision test online, you should make an appointment with an optometrist to take a test, just to make sure the test and results are accurate.

Because colour blindness is usually genetic, it is also possible to test for it using DNA. It is possible to diagnose colour blindness in babies and toddlers using DNA before they can speak.

Colour blindness is carried on the X chromosome, which is why it is more common in men than women. A child born male only needs to inherit one X chromosome with the carrier gene to be colour blind. A female, however, would need to inherit two X chromosomes with the carrier gene.

Living with colour blindness

Unfortunately, colour blindness is a lifelong condition and there is no cure. However, you can still adapt and go on with your everyday life, even with the condition.

Many people live their entire lives without realising they are colour blind. However, it can affect our everyday lives sometimes. If you are living with colour blindness, you may struggle to read information signs and warning signs that rely on colour coding. You may also find it harder to tell when fruit is ripe or when meat is cooked. Colour-blind children can struggle in the classroom if teaching materials are colour-coded, so teachers should be made aware of this and adapt the materials.

If you’re colour blind, different colours may appear as just subtle differences in shading. Good quality indoor lighting can make it easier to distinguish them. Special lenses are also available, which can help you to distinguish better between red and green.

If possible, try to ask somebody such as a friend or family member for help when checking that food is safe to eat, or with choosing clothing. If this isn’t possible, there are mobile phone apps that you can use to identify colours, and many websites have accessibility settings to make them more usable for colour-blind people.

Often, colour blindness does not significantly affect our lives, but finding out about a colour vision defect early in life means you can adapt quicker. This includes help with making classroom adaptions, career choices and other lifestyle adaptions before they become problematic.

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Colour blindness

Testing for colour blindness

Living with colour blindness

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