In colour blindness disease no any colour blindness actually exists but it is a colour vision deficiency disease. In this disease the person’s colour spectrum gets narrowed, so he becomes disable to perceive all colours rightly.
In human eyes there are three types of cones for three main colour perceptions and each cone is to sensitive to a certain wavelength of colours like red, green and blue. If the sensitivity of such cones gets shifted even slightly towards another one, colour blindness is caused. This disease is of certain types like green, blue and red disorders. If a person has red-green colour blindness, he can be confused on separating blue and purple colours as he cannot recognize red colour present in purple.
Such diseases are usually transferred genetically from the mother’s side. However diseases like glaucoma, ageing, alcoholism, injury on head, diabetes, and multiple sclerosis can also give birth to colour blindness.