Colour+Blind


 * Colour blind? No, you are just a shade different**

Tests on people who are colour blind reveal that they see a variety of colours as rich as those with normal sight, research has found.

Scientists investigated the most common form of colour blindness which affects six per cent of men, who are described as "green weak".

They found support for an idea that dates to the Second World War that they are better at penetrating camouflage. Men who have this form of colour blindness are poor at noticing small differences in the red, orange, yellow and green region of the spectrum. Some colour blind people are also unable to see the number 56 in the picture on this page. This form of colour blindness, known as deuteranomaly, enhances the perception of some colours outside the usual palette of descriptions. The findings are in a study, published today in the journal Current Biology, by Prof John Mollon, Jenny Bosten and Jo Robinson, of Cambridge University, and Dr Gabriele Jordan, at the University of Newcastle Upon Tyne.+

The team asked deuteranomalous and "colour-normal" individuals to rate the differences between pairs of colours that were predicted to look different to deuteranomalous men but to appear the same to those with normal colour vision. A statistical analysis of the results suggested that people who are colour blind live in a world with a "colour dimension" that is inaccessible to those with normal vision. The authors said that for those with normal sight "it was striking to watch a deuteranomolous subject giving large difference ratings to apparently identical stimuli, and doing so without hesitation".

Prof Mollon said that, in one sense, we are all colour blind. Surfaces present an infinite variety of reflection spectra. But our colour vision depends on just three types of colour sensor in our retina. Anomalous men also have three cones but one of them has a peak sensitivity that is shifted from the normal position in the spectrum.