What is colour blindness?

Eyes have two types of light-sensitive cells rods and cones. Rods help us see shades of grey. Cones help us see colours. People with colour blindness have defective cones. It also happens that information gathered by cones may not be conveyed properly from the eyes to the brain. In both cases, colour blindness is the result. Colour blind people commonly find it difficult to distinguish between red and green.