In the human retina, there exist both rods and three types of cones. The rods are chiefly the receptors that respond to light levels, while the cones send colour to the brain for interpretation.
An absence or slow development of these colour receptors is what is termed ‘colour blindness.’ Colour blindness can also be acquired through damage to the retina, optic nerve, or specific areas of the brain, though when acquired, it can actually manifest as a colour blind “spot” on the eye, having complete colour vision outside of that spot.
To say that colour blindness is an absence of colour is not so true for humans. In fact, total colour blindness, seeing life as a black-and-white television show, is extremely rare. Even rarer so is it that colour blindness occurs in females. What it really should be commonly known as is colour deficiency.
The most common in colour deficiency is a hereditary red-green type, which is actually a generalisation. What it aims to scratch at are two specific classifications. One such term is Protanopia, and that means a difficulty in distinguishing differences between red, yellow, and green, as they can often appear all to be yellow or brown.
For example, the first picture is that of rainbow stripes.
And this is the same picture as if see with the condition Protanopia.
