Correct Option: C

Colour-blindness is the inability to distinguish the differences between certain colours. This condition results from an absence of colour-sensitive pigment in the cone cells of the retina, the nerve layer at the back of the eye. A person with colour-blindness has trouble seeing red, green, blue, or mixtures of these colours. The most common type is red-green colourblindness, where red and green are seen as the same colour.