Colour-Blindness

We can see colours because we have light-sensitive nerve receptors in our retina called cones.
There are three kinds of cones, each able to detect red, blue or green light. (All the other colours are made up of a mixture of these three.) Some peope have faulty cone cells which means they can't easily tell the difference between one colour and another. When this happens, it's called colour-blindness.

Most people with colour-blindness have special problems with the colous red and green. This is called 'red-green colour-blindness' or 'daltonism' and for a reason that no one understands it affects men much more than women.

Another form of colour-blindness is total colour-blindness or 'achromatic' vision, but this is rare. People who are totally colour-blind can't see colours at all but see everything in shades of grey. For these people, the world is like a black and white movie. Both types of colour-blindness are hereditary.