Colour Vision

Colour Vision

People with colour vision deficiency are unable to see colours clearly and accurately. They may find it difficult to distinguish between different colours.


Colour vision deficiency is often called ‘colour blindness’. However, actual colour blindness, where no colour seen at all, is rare. People with colour vision deficiency may have difficulty identifying pale colours or deep colours if the lighting is poor.

Colour vision deficiency can vary in severity. Some people are unaware they have a colour deficiency until they have a colour vision test. Others will experience a very slight difference in the way they appreciate different hues and shades of colour. In rare cases, a person may experience many colours that all seem the same.

Types of colour vision

There are two main types of colour vision deficiency:

  • red-green deficiency – where people are unable to distinguish certain shades of red and green; it is the most commonly inherited type
  • blue-yellow deficiency – this is a rare condition where it is difficult to make a distinction between blue and green, and yellow seems a pale grey or purple

Why do you get Colour Vision Problems?

In most cases, colour vision deficiency is inherited from your parents (in your genes). But can also develop as a result of disease or because of medicines taken.

Genetic colour blindness (as it’s known) is due to a fault in the lining of the back of the eye (retina); here one of the colour detectors is missing or does not function normally.

How Do I know if I have Colour Blindness?

Most people know they have a colour vision problem if they cannot name colours correctly.  A child  may have difficulty naming colours or adults struggle to read a map or a document. However, in mild cases, colour deficiencies may go undetected.

The problem for diagnosis is that someone with a colour vision defect may see a snooker table as a different colour from someone with normal colour vision, but both will call the colour they see as ‘green’. But, and here is the problem, the colour that a person with colour blindness sees is  ‘yellow’.  How would you know the difference? It’s like teaching a child that the word for chair is the word ‘fire’; until that child asks for a fire to sit on we don’t realise there’s problem!

Does it Matter if I have Colour Vision Problems?

It is important to identify colour vision deficiency early as a child’s learning experience relies heavily on the use of colour.  Later on in life it could affect the type of employment choice that a person may make, for example, and I use the obvious one here, an electrician may have difficulty distinguishing certain colours or using colour discrimination for various choices may have unexpected or even dangerous outcomes.

I do not think that traffic light signals are an issue even though green and red are opposites (stop and go). The placing of the lights makes it easy to see which light is on and which is not; but certain jobs, such as pilots and air traffic controllers, exact colour recognition is imperative.

Colour vision tests

Colour vision tests are usually part of an optometrist assessment (Specsavers for example) and these tests show up sight defects.  Most people though do not go to an optometrist (when did the word change from an optician, answers on a postcard?) until they have a vision problem – so the issue could only arise when you fail an eye test for an important job and click here.
There are several tests for checking colour vision. In an occupational health setting the Ishihara test is usually the test of choice. (said Ish-ee-har-ah named after the Doctor who developed the test)

Ishihara test

The Ishihara test is the most commonly used test for checking colour vision. It uses plates (researched based and produced pictures in a book) made up of multi-coloured dots. Some of the dots will be a different colour and depict a number. See picture 12 at the top. Individuals look at the plate and say if they see a number.  Numbers you have difficulty identifying will be noted.
Different Ishihara plate tests are used to detect various types of colour vision deficiency. The most common test detects a red-green deficiency,  which is where most people have difficulty.

You may have a colour vision deficiency if you have problems completing the Ishihara plate test.

The tester should have stored the book in a place where the sunlight or use has not faded the pictures – this is especially important when a failed test means that you may have to change careers or job.  Ishihara books should be replaced with new every three years.

Arrangement test

The arrangement test involves arranging coloured objects in order of their different hues.

For example, coloured blocks of slightly different shades need to be organised from lightest to darkest. A particular pattern of mistakes could show you have a colour vision deficiency.

Occupational Health Test Procedures

For the test by occupational health, you will need to take your ordinary spectacles with you to use during the test.  Coloured lenses are not permitted.  The room light should be good and the test done in a quiet place.  Look at each plate for 4 seconds – longer than this or hesitation suggests that there is a problem with reading the correct number.  Do not try to learn the plates as the tester may show the plates in a different order.

Treating colour vision deficiency

There is no cure for inherited colour vision deficiency because it is not possible to repair or replace the cone cells in the retina.

However, as colour vision deficiency does not cause any long-term health problems, treatment is not essential to lead a normal, healthy life.

If you have colour vision deficiency as a result of a pre-existing health condition, or from taking a particular type of medication, it may be possible to improve your symptoms, either by treating the underlying condition or by using an alternative medication.

Most people with colour vision deficiency learn to adapt to their situation, and it is usually possible to find ways to compensate for difficulty with colours.

What Happens if I Fail my Colour Vision Test?

In the workplace, an operational assessment may be recommended if your job depends on distinguishing certain colours – for example a work test using the coloured objects as above to see if you can pick the correct object or make a correct decision.

For work where colour vision is essential to health and safety or product safety, there may be a problem with you being able to do the job.  The employer will try and adapt the workplace for you or even take the part of the job that includes the need to distinguish between colours out of the job but if that is not considered practical, then you may have to consider working elsewhere.

If you want to know if you have a colour discrimination problem…..

So if you know your parents are colour blind or you are considering a job where colour perception is important –  get a test done now.  Remember, though, if you try an online test from YouTube, there is no guarantee that your screen colours are correct or the tests are scientifically accurate.  Ask your company Occupational Health service for a colour vision test or consider paying for a full test from your optometrist or optician.  Shop around though because costs can vary.  To find your best option:

  • See here for more information on eyesight testing in the NHS and if you are eligible for a free test
  • Also, try Tesco,  Boots, Specsavers, Optical Express or a local optician many offer free eyesight tests.
  • If you are a computer user under the Display Screen Equipment Regulations, you must be offered a test by your employer too.  For more information click here

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