There are different types of colour blindness and in extremely rare cases people are unable to see any colour at all, but most colour blind people are unable to fully ‘see’ red, green or blue light. The most common forms of colour blindness are collectively known as ‘red/green colour blindness’. Although ‘red/green colour blindness’ is a common term, there are different types and severities. There is a huge myth that people with colour blindness
None of these statements are true! Being ‘red/green colour blind’ means people with it can easily confuse any colours which have some red or green as part of the whole colour. So someone with red/green colour blindness is likely to 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 above to understand this effect. For more information about the different colour combinations which cause the most problems, see Types of Colour Blindness. Problems can arise across the entire colour spectrum potentially affecting perception of all reds, greens, oranges, browns, purples, pinks and greys. Even black can be confused as dark red, dark green or dark blue/purple. The best way to understand colour blindness is to compare the ‘normal’ and simulated images throughout our website. The effects of colour vision deficiency can be mild, moderate or severe and people with severe forms often think that their condition is mild and doesn’t really affect them. Approximately 40% of colour blind pupils leave school unaware that they are colour blind, 60% of colour blind people are likely to experience problems everyday and yet often not realise the full impact. 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 (although they may correctly guess more using their sub-conscious coping strategies). As they rely heavily on coping strategies, colour blind people often think they have correctly identified a colour because it appears to them as the same colour as other things which they know to be a specific colour. However, coping strategies aren’t always reliable. A common surprise for colour blind people is the discovery that peanut butter ISN’T green (it’s brown). Depending upon which type of the condition a colour blind person has, they could see the set of pencil crayons similarly to the following images. The short answer to this question is simple: genetics. As with most things, the answer is rarely that simple. First of all, “color blind” is not a single thing. There are several different forms of color-blindness, and within each type, there are several forms. To understand color-blindness, you have to know a little about how we see. There is a thin layer of tissue at the back of the eye with millions of photo receptors. These photoreceptors have two shapes, rods and cones. Rods, of which there are vastly more of than cones, are responsive to dim light, making them useful for night vision or seeing in dark rooms. Cones are responsive to bright light. While the rods are all the same, all seeing the same colors, there are three different types of cones. These three types of cones allow us to see colors across the spectrum from those colors with long wavelengths, like red, medium, like green and short wavelengths like blue or violet. Parenthetically, colors with longer wavelengths then visible red colors are “infrared” while colors on the other end of the scale are “ultraviolet”. There is a piece of trivia that will impress (or bore) your friends. Color-blindness is when something goes wrong with one of the cones and the person cannot see certain colors correctly. The most common form of color-blindness is called “red-green color-blindness”, which is a loss of, or limited function of, the red cone. This is the form that is way more common in men. As we mentioned, it was all in the genetics. The information for the red cone is in the X chromosome. Men only have one X chromosome, so of the genetic code is messed up, there is no back up. Women on the other hand, have 2 X chromosomes, so even if one has the code that leads to color-blindness, it is usually offset by the good gene. In this case, as with all X-linked inheritance, the mother can be a carrier, and can pass that mutation to her children, but she, herself, will not be affected. Oddly enough, women who have the gene that would lead to red-green color blindness, or other vision related mutation, have a slight chance of being tetra-chromatic. What’s that? Well, with 3 types of cones, humans are tri-chromatic. Each cone seeing a vast amount of colors, in all of the possible combinations, we can see about 7 million different colors. Since women have 2 X chromosomes, for each gene, one is generally not used. For some women who have some form of mutated cone, it could lead to a 4th distinctive cone. Adding a 4th cone and all of the colors that it could see to the 7 million colors most people could see, a tetra-chromatic woman can see upwards of almost 100 million colors.  There are two other forms of color-blindness which are extremely rare: Blue-Yellow, which is a problem with the blue cone and complete color blindness where the person cannot distinguish any color except shades of grey, like a black and white television. These are caused by genes which are carried equally by men and woman, so while extremely rare, neither of these are sex-linked. |
