Box of delight

The human eye can physically perceive millions of colours. But we don’t all recognise these colours in the same way.

Some people can’t see differences in colours – so called colour blindness – due to a defect or absence of the cells in the retina that are sensitive to high levels of light: the cones. But the distribution and density of these cells also varies across people with “normal vision” causing us all to experience the same colour in slightly different ways.

Subjects identified the left-hand image as a woman and the right-hand one as a man. Yet the two images differ only in skin tone. Study by Richard Russell, Sinha Laboratory for Vision Research, MIT.