What is colour blindness and who does it affect?
What is colour blindness?
Colour blindness, or colour vision deficiency, is the inability to perceive colours normally. Although it is one of the world’s most common genetic conditions, affecting millions of people, it is generally under-recognised and unsupported.
Within the retinas at the back of our eyes we have specialised nerve cells called cones which help us to perceive colour. There are three different types of cone cells which absorb red, blue or green light. These cone cells work together to enable us to see millions of colours, but in colour blindness one of these cone cell types does not function properly. About 25 per cent of colour blind people have one cone type which doesn’t function at all.
People with normal colour vision can see the full visible spectrum but people with colour blindness cannot see many colours and often confuse different colours because to them many distinct colours appear to be the same, for example blue and purple.
Who is affected?
Worldwide, more than 300 million people have some form of colour blindness – that’s similar to the population of the USA.
Of the 250 million unique viewers who watched Rugby World Cup 2019, approximately 12.9 million would have had some form of colour blindness (based upon a 62:38 male:female ratio spectator profile).
Put in another way, and using the same male:female ratio, in an average national rugby stadium such as the 72,000 seat International Stadium Yokahama in Japan, venue for the Rugby World Cup 2019 final, approximately 3,700 spectators will be colour blind.
What causes colour blindness?
The technical term for colour blindness is colour vision deficiency (CVD). It is usually an inherited condition caused by ‘faulty’ gene-sequencing in the DNA of the X-chromosome. Colour blindness can also be acquired as a side effect of some diseases, for example diabetes, multiple sclerosis and sickle cell anaemia and from some drugs (including heavy use of alcohol) and some medications. Colour vision also declines with age from around 65 years.
The three types of cone cells in the retina absorb red, blue and green light respectively and send electrical signals to the brain. The brain combines the electrical signal information from the cone cells allowing people with ‘normal’ colour vision to see in full colour. Normal colour vision is also known as trichromacy.
In colour blindness, one of the cone cell types does not operate normally so the brain confuses the electrical signals. There are three main types of genetic colour vision deficiency (CVD) which can vary in severity.
Types of colour blindness
In less severe forms of colour blindness (known as anomalous trichromacy) all cone types exist but one of the cone types does not function normally. Severe colour vision deficiency is known as dichromacy and in people with dichromacy one of the cone types does not function at all.
- Protan deficiencies relate to inability to perceive reds normally
- Deutan deficiencies relate to inability to perceive greens normally
- Tritan deficiencies relate to inability to perceive blues/yellows normally
Monochromacy is complete colour vision loss, where people will see only in greyscale. This condition is extremely rare and usually related to other vision problems.
For a detailed explanation of the different types of colour blindness refer to Definitions.
All severities of inherited red/green CVD types are very common. However, blue/yellow deficiency and monochromacy are extremely rare.
Acquired colour blindness is more likely to affect blue/yellow vision and in some cases can be cured. There is no cure for inherited colour blindness.
Colour blindness – myths busted
- Red/green colour blindness is not a single condition
- People with red/green colour blindness do not only confuse reds with greens
- People with red/green colour blindness do not see red as green and green as red
- People with red/green colour blindness can see blue and yellow clearly
- Hardly anyone with colour blindness sees only in greyscale, most people with colour blindness can see many colours
- Colour blind people can identify many colours but do not see them in the same way as people with normal colour vision do
People with red and green types of colour blindness have many symptoms/colour confusions in common because the red and green cones are sensitive to light wavelengths which are close to each other on the visible light spectrum. Therefore, because many colour combinations cause confusion for people with both red and green colour vision deficiencies, red/green colour blindess is often mistaken as a single condition.
How do colour blind people experience colours?
How colour blind people experience colours depends upon several factors, such as the type and severity of their CVD and the light conditions in which they are viewing them.
Colour blind people do not all see colours in the same way as each other. Some people with CVD do not find that their condition causes them too many problems in everyday life, while people with more severe colour blindness face daily frustrations and challenges.
People who are colour blind know the colours of everyday objects even though they may not experience them in the same way that people with normal colour vision do. They will know, for example, that the sky is blue and grass is green but they may mistake the colour of an object or not see a difference between colours in some combinations. Those same colours will appear to be very different to people with normal colour vision, for example someone with normal colour vision would not confuse greens with reds.
To complicate matters, lighting can also affect how someone with colour blindness identifies colours. For example, a red object could appear as brown in low light conditions/shadow or as orange or green in bright sunlight.
In simple terms, someone with red/green colour blindness may find it difficult to perceive the red or green elements in many different colours. Thinking about the colour purple, this is made up of a combination of blue and red. If you are not able to easily distinguish red then you will only see the blue when you look at purple. This is why most colour blind people confuse blues and purples.
In the Show Your Shirt images above reds, greens, browns and oranges appear ‘dirty’ green, and purples appear the same as dark blue, but notice how blues and yellows stand out. This is because people with red/green deficiencies can see blue and yellow similarly to how people with normal colour vision do.
Numerous different colour combinations can cause confusion. Some shades of red and green can be mixed up while others can be easy to tell apart, but this is due to differences in contrast rather than ability to tell colours apart by their hue.
The most common problems for people with red/green colour blindness are with telling the difference between:
- reds/greens/browns and oranges
- blues/purples and dark pinks
- pastel colours
- bright orange/bright green and yellow
But plenty of other colour combinations can cause problems. For example, someone with a red vision deficiency will find it difficult to read black text against a red background.
The most common colour confusions for people with blue/yellow CVD are light blues with greys, dark purples with black, mid-greens with blues and oranges with reds.
How can gender and ethnicity affect colour blindness?
Approximately one in 12 men (eight per cent) inherit red/green colour blindness but only one in 200 (0.5 per cent) of women do.
Colour blindness is very common in men because it is carried on the X-chromosome. Men only have one X chromosome, but women have two. If a man inherits colour blindness (on his X -chromosome, which he receives from his mother) he will be colour blind.
For a woman to have red/green colour blindness she must inherit colour blindness on both of her X-chromosomes. This means her father will be colour blind.
Inherited blue/yellow colour blindness can affect men and women equally because it is carried on a different chromosome.
Why are white men more likely to be colour blind than people from other races?
The risk of being colour blind varies with ethnicity and red/green types of colour blindness are more common in people of North American and European descent. The reasons for this are not yet fully understood. Scandinavian men have the highest chance of being colour blind (more than one in 10), while people from sub-Saharan Africa and indigenous populations have the lowest chance.
In Asian countries the incidence of colour blindness is slightly lower than in countries derived mainly from people of European and North American backgrounds, at around one in 20 men (five per cent) and one in 200+ women.
Why are some colour blind people unaware they are affected?
Colour blind people can see clearly and in focus and can see some colours clearly, for example blue and yellow. Unless they have monochromacy (greyscale vision) ‘colour blind’ people are not blind to all colours but they will never have experienced normal colour vision, so they often don’t realise how much information they can miss. This means they might not realise they do not see colours in the same way as others.
Imagine permanently wearing tinted sunglasses. You would soon get used to seeing the world with a slightly different colour tint. For the most part you will be able to carry on living your life as you would without wearing sunglasses, but some colours will appear differently to the way they appeared before. Colour blindness is a more extreme version of this effect, as demonstrated in the simulated images throughout this document.
People with severe colour blindness are more likely to be aware they have a CVD but may never have been formally diagnosed and they often believe their condition is mild.
As colour blind people grow older, they learn coping techniques to help them distinguish between colours. The milder someone’s colour blindness the fewer challenges they are likely to face day-to-day. Sometimes colour blind people will talk down the impact of their condition to protect themselves from potential discrimination.
I am colour blind, how can I understand what others see in the ‘colour blind simulations’?
Colour blind people are often unaware that there are different types and severities of CVD and that other people with CVD do not see in the same way they do. If you are colour blind not all of the simulated images in this document will appear to you to be the same as the ‘normal’ vision images and this will mostly be because you have a different type/severity of colour blindness to the condition being simulated. The simulated images in this document are mainly types of red or green CVD because these are the most common types, so you may not easily see any differences between the sets of images, but to get an idea of what the red/green simulated images are demonstrating to people with normal colour vision, have a look at the simulations for ‘tritanopia’ below and compare how you see the tritanopia simulation and the ‘normal’ versions of the same image.
This should give you a better idea of how differently the red/green colour blind simulations can appear to the ‘normal’ images for people with normal colour vision. Your condition is as shocking for people with normal colour vision to see as the tritanopia simulation is for you to see, probably even more so. Concentrate especially on the yellow shirt in the middle.
The image on the right below shows normal colour vision (Australia in yellow) but in the tritanopia simulation on the left, the yellow kit appears to be almost white both to people with normal colour vision and to people with red and green types of colour blindness.
Who might be affected by colour blindness in rugby?
Colour blindness can affect anyone involved in rugby, including spectators, players, match officials, coaches, pitch-side care providers, support staff and administrators, as well as people who work in supporting roles such as the emergency services, media, catering or sponsors.
In a typical male squad of 32 players, statistically there will be two or three players with colour blindness. Many people reading this guidance will have a colour vision deficiency.
Why are people affected differently in different situations?
The images chosen in this document to demonstrate how colour blind people might see certain rugby situations are generally of the severe form of one type of colour blindness. Therefore, depending upon someone’s exact type and severity of colour blindness, the ‘normal’ and simulated images may appear to be exactly the same to them or very different. The personal testimonials throughout this document demonstrate that not all people with colour blindness have the same experiences in rugby and this is due to their type of colour blindness and how they are affected by specific circumstances, including lighting conditions.
"Things look worse for me on the computer and the TV screen than they do live, the main example being the red vs green Ireland vs Wales games. I never really had a major problem when I was on the line in the Six Nations for that game but, watching it on TV now, it’s a big problem for me. That game is one example, but any red/green football or rugby clash, I just know it’s going to be a difficult watch on TV."
"People do switch off if they can’t differentiate the teams. I know Wales v Ireland is a big problem for many colour blind, people but it’s not a problem for me. However, I noticed the second they ran out in the Glasgow v Cardiff Pro14 game [October 2021] that it was going to be an issue. That game gave people with normal colour vision a taste of what it is like to struggle with colours and numbers on kits."
The Champions Cup match was a great example to demonstrate to people with normal colour vision what it can feel like to colour blind people when they experience a ‘colour blind’ kit clash game, either as a player or a spectator.
"We kind of had a game plan of who we guarded, and it got easier as the sun went down, but at first, with the sun in my eyes, the jerseys looked the same to me."
How can I help?
As there are many types and severities of colour blindness it might seem daunting to try to make changes to cater for all types, but fortunately colour blindness is generally an easy condition to support – simply maximising contrast between colours, or sometimes just adding an additional means of giving the information, such as labels or symbols, can be an effective solution for everyone affected.
For example, in the situation discussed by Dave Pearson above, the solution would be to ensure there was enough contrast between the two kit colours. A simple to way to work out if certain colour combinations have sufficient contrast is to think about how the colours might appear in greyscale. If they would appear similar, then there is unlikely to be sufficient contrast between them.
Please see the menu on the top left of each page of this site to find the sections of this guidance which are relevant to your rugby role or to find out more about providing support specific situations.