Why do we see colour?

THAT'S THE WHY:  Roses are red, violets are blue . . . and we humans realise this because we can see colour.

From rainbows to traffic lights, we register colours through light-sensitive cells called “cones” at the backs of our eyes, and those signals get processed by the visual cortex in our brains.

All very well and it surely makes our world a prettier place, but why do we see colour? Why, in evolutionary terms, did colour vision stick around?

A long-standing theory suggests it helped our ancestors pick out edible fruits and leaves.

But neurobiologist Dr Mark Changizi argues that maybe more importantly, our colour vision allows us to recognise changes in the appearance of the skin that are affected by blood flow and oxygen levels.

In his book, The Vision Revolution, he points out that we blush with embarrassment, blanch with fear and go purple when choking.

People with anaemia may have a greenish pallor, while bruises and aroused sexual organs can lend particular hues to areas of skin, too.

Thus skin can act as a “television”, providing an insight into another individual’s emotional and physical state, according to Changizi.

He suggests it as a factor in the evolution of our colour vision: “Our skin didn’t change to suit our eyes, but rather, our eyes changed in order to better see our skin.”

– CLAIRE O’CONNELL