This is a defect of the eye in which a person is unable to distinguish between certain colours (More especially to blue, red and green colours). This defect arises due to insufficient or no cone shaped cells, on the retina. There are three types of cone cells, one responding to blue colour, the second to red and the third to green colour. A colour blind person does not possess some cone cells that respond to certain colours. Colour blindness is a genetic disorder. There is no cure to this defect. A colour blind person can see everything clearly but is not able to distinguish between different colours. (A colour blind person may not be issued a motor driving licence as he or she may not be able to distinguish between green and red signals).