A person with a colour vision defect will confuse some colours (most common is red and green).
This is most commonly an inherited problem with 1 in 12 males and about 1 in 200 women.
They can also be caused by diseases that injure the nerves in the eye.
It is very important to test children especially boys to ensure correct career choices are made later in life - for example if you have red colour deficiency you cannot be a commercial pilot.
