Colour Deficiency Symptoms People with colour deficiency have decreased ability to identify or distinguish certain colours. This is almost always detected through screening tests or recognized by parents, teachers or friends rather than the affected person himself / herself. Types There are many types of colour deficiency. The most common is red-green colour deficiency in which the person has a difficulty in distinguishing between purple and blue. A less common type is yellow-blue colour deficiency. People with colour blindness are unable to identify colours at all. Cause The light-sensitive cells in the retina are responsible for colour perception. If these cells are defective, they cannot receive or transmit the correct information to the brain. Red-green colour deficiency is usually inherited. Other types, especially the yellow-blue type may be related to eye diseases. Colour blindness is a congenital defect. Incidence Red-green colour deficiency is the most common type. It is more common in men than in women. About 8% of men are affected compared to 0.4% of women. Colour blindness is rare. The incidence is about 1 in 1 million population. Management It is recommended that all children should have their colour vision tested because the affected child may not realize the problem. They think that they see as normally as other children. Colour deficiency is a life-long condition. Depending on the severity and type of colour deficiency, the affected person may experience some problems in daily life and in choosing his/her career. Although there is no effective treatment, most people can adapt to the condition through counselling.