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 world. In Britain this means that there are approximately 3 million colour blind people (about 4.5% of the entire population), most of whom are male. Worldwide, there are approximately 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 the vast majority of people with deficient colour vision the condition is genetic and has been inherited from their mother, although some people become colour blind as a result of other diseases such as diabetes and multiple sclerosis or they acquire the condition over time due to the aging process, medication etc.

Normal Vision Tritanopia

Most colour blind people are able to see things as clearly as other people but they are unable to fully ‘see’ red, green or blue light. There are different types of colour blindness and there are extremely rare cases where people are unable to see any colour at all.

The most common form of colour blindness is known as ‘red/green colour blindness’ and most colour blind people have one type of this. Although ‘red/green colour blindness’ is a common term, there are different types and severities of it. Being ‘red/green colour blind’ doesn’t mean people with it mix up red and green only, it means they can mix colours which have some red or green as part of the whole colour. So someone with red/green colour blindness will probably 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 below to understand this effect. For more information about the different colour combinations which cause the most problems, see Types of Colour Blindness.

Normal Vision Deuteranopia

Similar problems can arise across the whole colour spectrum affecting all reds, greens, oranges, browns, purples, pinks and greys. Even black can be confused as dark green or dark blue.

The effects of colour vision deficiency can be mild, moderate or severe so, for example, approximately 40% of colour blind pupils currently leaving secondary school are unaware that they are colour blind , whilst 60% of sufferers experience many problems in everyday life.

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. Depending upon which type of the condition a colour blind person is suffering from they could see the set of pencil crayons similarly to the following images.



Normal Vision Deuteranopia Protanopia Tritanopia





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