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Colour-blindness: The forgotten disability

Updated on January 21, 2010

Is colour-blindness a disability?

It is a genetic defect*, it is an inherited anomaly, it can't be corrected by prosthetics or mechanical aids, and it has an impact on the person's life and prevents them doing certain things. The person has a disability. Unfortunately it is slightly intangible. It isn't obvious like blindness or deafness or using a physical aid such as a wheelchair.

Colour-blindness therefore is not generally perceived as a disability, and is of only passing interest to other people if the sufferer mentions they have inherited the condition. But in reality how many people are affected? Percentage wise, colour-blindness affects one in twelve males, and one in 200 females. This means therefore, that in a city the size of Greater London, for instance, with a population of around seven and a half million, there are going to be in excess of 330,000 people affected by the condition in one form or another. In New York that's going to be more than 366,000. So these are not insignificant numbers, and theoretically at any one time Central Park could be filled with colour-blind people strolling about and wondering why on earth there are so many words for "green"!

*Note: There are also some types of colour-blindness which are not genetic or inherited, but can be caused by head trauma injury or by retinal exposure to ultraviolet light. It can also be one of the effects of the onset of diabetes. Some of the forms of colour-blindness caused by injury can be treatable.

The technical stuff.

The term colour-blindness is actually a slightly inaccurate term for this inherited condition. There is no actual "blindness" involved - it's more a sort of colour confusion, and colour-blind people do not see in black and white, except in some very rare and extreme cases.

People with normal colour vision are "trichromats". That is, the receptors in the retina of the eyes process light as a blend of all three primary colours. Colour-blind people are dichromats, and can only process colours using a blend of two out of the three primary colours. Which two primary colours used dictates the type of colour vision defect that person has, and there are several different types the commonest being the red/green type, and the one most people have heard of.

Early pioneering work in the field, prompted by his own colour-blindness, was done in the eighteenth century by English physicist John Dalton. His first paper, “Extraordinary Facts Relating to the Vision of Colours”, was published in 1794 and ascribed the lack of colour perception in a subject to a discolouration of the liquid medium of the eyeball. These were just the first steps in investigation of a subject that had not even been formally described by scientists until Dalton wrote about his own condition. In fact the thoroughness and depth of Dalton’s scientific research into the subject led to “Daltonism” becoming a general term for the condition. In 1995 a scientific examination of his preserved eyeball demonstrated that he in fact had deuteroanopia, a more rare form of colour-blindness in which the cones sensitive to medium wavelength colours are missing, rather than the more common deuteroanomaly which perceives colours in a mutated form, so that he was only able to perceive the blue, purple and yellow part of the spectrum.

Testing for Colour-blindness

Dalton’s deuteranopia was in fact just one type of a whole range of colour perception defects, much broader than many people imagine. In the 200 years since Dalton first described the condition the different types Protanomaly, Deuteranomaly, Dichromasy, Protanopia, Deuteranopia, Tritanopia, Protanomalous Trichromatism, Deuteranomalous Trichromatism, Tritanomalous Trichromatism, and Monochromatism have all been identified and described, and it was discovered that, while in some forms of colour-blindness some of the retinal cones are less sensitive to certain colours or see mutated versions, in other forms of the condition cones are missing altogether.

Following on from the realisation that the subject was much broader and more complex than was first thought, a range of diagnostic tests for the condition were developed, the most well known being the circles filled with multi-coloured dots of the Ishihara test. First published in 1917, the Ishihara Plates were developed by Dr. Shinobu Ishihara of TokyoUniversity as a test for red-green colour deficiencies. This test not only identifies a red-green anomaly, but also gives an indication of the severity of the condition.

Ishihara test plate

One of the test plates developed by Dr Ishihara. In this plate a person with normal colour vision will see the number 74. Persons colour deficiency will see the number 21, as I do, while some viewers with a more extreme condition may see nothing.
One of the test plates developed by Dr Ishihara. In this plate a person with normal colour vision will see the number 74. Persons colour deficiency will see the number 21, as I do, while some viewers with a more extreme condition may see nothing.

Colour-blindness and the web

The internet is now used by a very high proportion of people on a daily basis, and because of the percentage of people in the world affected by colour vision deficiencies, there is a probable likelihood that one internet user in twenty will have difficulties with reading colours on a screen. This is something that website builders must take into account, because if a potential customer visiting a new site has trouble reading type against the wrong colour background, for instance, or in very bad cases finds it physically tiring to try to read a web page, they will very quickly click off that page and look for another, better designed site. By not considering the colours used in a web page design, there is the distinct possibility of losing one out of every twenty visitors to the site.

Useful tools

The one advantage to working in the virtual world is that all colours have a designation and are detectable, unlike in the real world where matching a paint swatch to a painted wall is a physical impossibility to anyone with colour vision deficiencies. In the world of computers every colour carries a hexadecimal code to identify it. If, like me, you are a colour-blind graphic designer (if that’s not a tautology!) this means that we can always match colours perfectly, and there are a number of computer tools that help us do this.

My favourite, and one I use a lot, is a multi-purpose colour-picker program called Color Cop. This is a free download software package written by Jay Prall, which runs as a standalone window on your computer on top of all other programs or windows that are open. It has a colour-picker which can select any pixel on the whole screen including icons, system tray and toolbars, and gives an RGB readout and the hexadecimal code of the colour its reading, and also shows a blow-up in a small separate window of what the colour-picker sees. This makes it possible to match colours perfectly even working between two completely different graphics programs. We still don’t know what the colours are, but we know they match!

Color Cop colour-picker tool

Download a really useful free colour-picker tool to accurately match hexadecimal codes. Click link above.
Download a really useful free colour-picker tool to accurately match hexadecimal codes. Click link above.

How colour deficient people see

The image on the left shows how a person with normal colour vision sees a scene. The image on the right is a simulation of how a dichromat sees the same scene.  Images courtesy of Terrace L. Waggoner's Colorblind website
The image on the left shows how a person with normal colour vision sees a scene. The image on the right is a simulation of how a dichromat sees the same scene. Images courtesy of Terrace L. Waggoner's Colorblind website

Living with colour-blindness

One of the most useful things you can do is marry someone with good colour vision! Okay, a bit out of your control, but if it happens – brilliant! It helps a lot.

So what’s it like living with a colour vision deficiency? Well the weird thing is that for us it’s normal. It’s the rest of you that seem to insist on using far too many names for the colours! However, there are definitely things the colour-deficient person can’t do.

If your kids are fair skinned and they’re out in the sun, you won’t notice that they’re becoming sunburnt until it’s far too late. Subtle changes in skin colouration just can’t be seen.

Similarly if a friend or partner is pale due to oncoming sickness, you won’t see that either.

You also can’t see the pinkness in undercooked meat, which could be vital in the case of chicken.

You can’t get a job as a pilot or an ambulance driver.

A dichromat would also be a very poor witness to a hit and run accident or a robbery when asked to describe a getaway vehicle or put together a description of a perpetrator with colour of hair, eyes and clothing.

On a positive note, dichromats were used during the war to penetrate camouflaged locations as it was thought that their disability enabled them to pick out the man-made colours against a natural background.

In the same vein it is thought that early man would have a distinct advantage while hunting if he had a colour deficiency. The dichromat among a hunting party would spot the prey early and would bring back the first food, ensuring that his family always ate. In this case the dichromacy would be perceived as a mutation for survival. In the same way it could be seen that the fact that very few females are affected, but are instrumental in passing on the gene, specifically selects the hunters for this useful condition, but not the non-hunting females.

Working with colour deficiency

You have to learn to work around a colour deficiency. Firstly, if it’s necessary for a particular task in hand, you have to inform those around you and they have to understand the realities of the situation and use language accordingly. For instance, if another person wanted to refer to a particular car parked in the street, a good phrase to use for a colour-blind person would be “the Ford parked behind that van”, whereas a very bad phrase would be “the green car over there”.

Helpful colour-coded charts are very bad news. The bane of my life are maps and tables that use colour-coding to identify points of interest. It doesn't work. For dichromats the information might just as well be in ancient sanskrit. We have a perfectly good system of arabic numerals developed around 500 AD by Indian mathematicians that have served us well for around 1500 years, so why replace them with a system that only works for some of the people? The more information that needs to be got across the worse it gets, because they use more and more colours, and the more colours they use the closer the hues get and the more unintelligible the chart becomes, and don’t even get me started on bottle banks! Why are there green and brown bottles? I’ve no idea which is which.

At the checkout when paying by credit card point out to the checkout person that it helps if they ask you to “put in your number and press enter”, rather than “press the green button” because often there are other colour buttons available and you end up confused.

Wrapping it all up

In conclusion I’d just like to put it into perspective in one sentence what it is like to be colour-blind. It’s not that you see the wrong colour – most of the time you just don’t know what the colour is.

I hope that helps. When people ask me “what colour is that car?” probably 90% of the time I don’t know and wouldn’t like to hazard a guess as to the name of the colour. As they say – what’s in a name?

And finally the trade-off. There should always be a little glimmer of light, and in this case you don’t get asked by your partner to choose the colours when redecorating!

Colour-blind awareness logo

My design for a colour-blind awareness logo. If you have a shop or similar, print it and display it for support.
My design for a colour-blind awareness logo. If you have a shop or similar, print it and display it for support.


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      4 years ago

      A very informative article. Thank you.


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