What is colour-blindness? What kind of retinal cells are lacking in person suffering from this defect?

What is colour-blindness? What kind of retinal cells are lacking in person suffering from this defect?

Answer:
The defect of the eye due to which a person is unable to distinguish between certain colours, is known as colour blindness. Cone shaped retinal cells are responsible for making a person differentiate between colours. The colour blind persons do not possess cone cells that respond to certain colours.