As with any other physical characteristic, the number of rods and cones will vary from person to person. This means that we will all interpret colour slightly differently. Try covering one eye and looking at something brightly coloured, and then does the same with the other eye.

Chances are your brain will get slightly different messages from each eye. These differences are generally small and fall within limits of a standard observer. There are, however,-a few people whose rod and cone distribution are such that colours vary significantly.

Most of our colour learning is at a very early age, grass is green, sky is blue, buses red, and we take mummy’s word for it and are blissfully unaware until taking a colour test. About 1 in 8 men and less than 1 in 100 women suffer colour blindness.

Red/green deficiencies are most common types where the visible spectrum appears to have been shortened, but blues and yellows are seen as brighter and more distinct with red and green as greys.