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What is colour blindness?

Colour (color) blindness (colour vision deficiency, or CVD) affects approximately 1 in 12 men (8%) and 1 in 200 women. In the UK there are approximately 3 million colour blind people (about 4.5% of the entire population), most of whom are male. Worldwide, there are estimated to be about 300 million people with colour blindness, almost the same number of people as the entire population of the USA!

There are different causes of colour blindness. For most colour blind people their condition is genetic, usually inherited from their mother, although some people become colour blind as a result of other diseases such as diabetes and multiple sclerosis or it can be acquired due to ageing or from taking drugs and medications.

Children in coloured shirts - Normal Vision Children in coloured shirts - Tritanopia

Normal Vision | Tritanopia

Pens - Normal Vision Pens - Deuteranopia

Normal Vision | Deuteranopia

There are different types of colour blindness and in extremely rare cases people are unable to see any colour at all, but most colour blind people are unable to fully ‘see’ red, green or blue light.

The most common forms of colour blindness are collectively known as ‘red/green colour blindness’. Although ‘red/green colour blindness’ is a common term, there are different types and severities. There is a huge myth that people with colour blindness

  • only can’t ‘see’ red and green
  • only confuse red with green, or
  • see reds as greens and greens as reds

None of these statements are true!

Being ‘red/green colour blind’ means people with it can easily confuse any colours which have some red or green as part of the whole colour. So someone with red/green colour blindness is likely to confuse blue and purple because they can’t ‘see’ the red element of the colour purple. See the example of pink, purple and blue pen cases above to understand this effect.

For more information about the different colour combinations which cause the most problems, see Types of Colour Blindness.

Problems can arise across the entire colour spectrum potentially affecting perception of all reds, greens, oranges, browns, purples, pinks and greys. Even black can be confused as dark red, dark green or dark blue/purple.

The best way to understand colour blindness is to compare the ‘normal’ and simulated images throughout our website. The effects of colour vision deficiency can be mild, moderate or severe and people with severe forms often think that their condition is mild and doesn’t really affect them. Approximately 40% of colour blind pupils leave school unaware that they are colour blind, 60% of colour blind people are likely to experience problems everyday and yet often not realise the full impact.

Statistically speaking most people with a moderate form of red/green colour blindness will only be able to identify accurately 5 or so coloured pencils from a standard box of 24 pencil crayons (although they may correctly guess more using their sub-conscious coping strategies). As they rely heavily on coping strategies, colour blind people often think they have correctly identified a colour because it appears to them as the same colour as other things which they know to be a specific colour. However, coping strategies aren’t always reliable. A common surprise for colour blind people is the discovery that peanut butter ISN’T green (it’s brown).  Depending upon which type of the condition a colour blind person has, they could see the set of pencil crayons similarly to the following images.

Find out more about the diagnosis of colour blindness
Find out more about the causes of colour blindness
Find out more about the different types of colour blindness