People with colour blindness (also known as colour vision deficiency) find it difficult to identify and distinguish between certain colours. This condition affects approximately 3 million people in the UK and it impacts 1/12 men and 1/200 women.

People with colour vision deficiency can see things as clearly as people without the condition and it is extremely rare for someone to be unable to see any colour at all. The most common form of colour blindness is known as ‘red/green’ colour blindness. The simple name is slightly misleading as there are various types and severity of ‘red/green’ colour blindness. This type of colour blindness doesn’t mean people mix up just red and green – it means they mix up colours which have some red or green within them. For example; people are likely to mix up blue and purple because they cannot see the ‘red’ element of the colour purple.

Someone with colour vision deficiency may:

  • find it hard to tell the difference between reds, oranges, yellows, browns and greens
  • see these colours as much duller than they would appear to someone with normal vision
  • have trouble distinguishing between shades of purple
  • confuse reds with black

In rare cases, some people have trouble with blues, greens and yellows instead. This is known as “blue-yellow” colour vision deficiency.

Here is an example of the difference between a ‘normal’ perception of colour and someone suffering from colour blindness

How is it caused?

Colour vision deficiency is most generally caused by genetics and is likely to be inherited from the mother. The NHS explains that ‘it occurs because some of the colour-sensitive cells in the eyes, called cones, are either missing or do not work properly’.

Occasionally, colour vision deficiency may develop later in life as the result of:

  • an underlying health condition, such as diabetes, glaucoma, age-related degeneration and multiple sclerosis
  • a side effect of a medication
  • exposure to harmful chemicals

Many people also find it more difficult to distinguish between colours as they get older. This is normally just a natural part of the ageing process.

Why does it impact men more? 

The National Eye Institute explains that ‘men are much more likely to be colour blind than women because the genes responsible for the most common, inherited colour blindness are on the X chromosome.’

So people with an x-chromosome and a y-chromosome (men) only need their one x to be defective to catch it. People with two x-chromosomes (women) need both to be defective.

How does colour blindness impact your life?

The impact of this condition can vary from mild to quite severe. Approximately 40% of colour blind pupils leaving secondary school are unaware that they are colour blind. However it can sometimes cause issues such as:

  • difficulty at school if colours are used to help with learning
  • problems with food, such as identifying whether meat is fully cooked or whether fruit is ripe
  • getting medications confused if they’re not clearly labelled
  • trouble identifying safety warnings or signs
  • slightly limited career choices – certain jobs, such as pilots, train drivers, electricians and air traffic controllers, may require accurate colour recognition

Overall, many people with a colour vision deficiency have few, if any, difficulties. They can do most normal activities, including driving.

Testing for colour blindness

The NHS recommends that you ask for a colour vision test at an opticians if you think you or your child may have a colour vision deficiency, particularly if it started suddenly or is getting worse. Colour vision tests do not usually form part of the routine NHS eye test, but you can specifically ask for them.

What are the tests?

Two of the main tests used to diagnose colour vision deficiency are:

  • the Ishihara test, where you’re asked to identify numbers contained within images made up of different coloured dots
  • colour arrangement, where you’re asked to arrange coloured objects in order of their different shades

There are a number of online tests using similar techniques that may help detect a possible problem, but it’s best to have a proper test at an opticians if you have any concerns about your colour vision.

Most people get used to it over time, it will not normally get any worse, and it’s rarely a sign of anything serious.