In the eye there are three kinds of colour receptor called the cones. One set generates red, a second generates blue and a third generates green. The other important receptors in the retina are the rods which bring about light and dark effects. Light enters the eye through the iris in the pupil of the eye, passes through the lens and strikes the white screen at the back of the eye called choroid process.

This reflects light into the rods and the cones and all this takes place in what is known as the retina at the back of the eye.

When the eye is focused on a wall of colours it passes over the reds which at first go blurred though instantaneously the lens changes its shape. The lens fattens to focus the colours precisely on the retina again whereas before, the rays would have tried to focus behind the retina. Such a change in the shape of the lens is the same as what takes place when the viewer is looking at something rather nearer than the wall of colours. It?s this phenomenon that makes red colours appear nearer.

Similarly, when the eye looks at the same wall and passes over the blue colours these now appear blurred because the blue rays are coming to a focus in front of the retina. This change in the lens is exactly the same as the way it changes when looking at something further away. Thus, blue colours on the surface of the wall appear to receed behind the wall. This is the reason why so many more blue cars have accidents than the cars of other colours. As long ago as 1968 this was reported by AA's magazine 'Drive'.

It is possible to follow the path of the colour-generating rays through the eye to the brain. The colour-generating rays from the right side of the field of vision enter the irises of both eyes and are focused on the left halves of the retinas of both eyes. These pass from the retinas to the optic nerves. The two optic nerves cross each other and the outcoming channels are called optic tracts and their crossing is called the chiasma. Past the crossing are the optic tracts which enter two colour processing organs called lateral geniculate bodies, where those impulses which have come from the right side of the field of vision divide up into an optic radiation to the back of the brain where the cerebral cortex is activated on the left side of the calcerine fossa in the striate area of genarii.