Some people see this dress as white and gold and others see it as blue and black. The dress is actually blue and black but this is irrelevant as the key question is why do some people see the dress in this photograph as one combination of colours and other people see it as another combination?

The best explanation I have found is that we have all evolved to remove the colour of the light around us. In the early morning and late evening the light is reddish and at midday it is blueish. So to enable us to see the ‘real’ colour our visual cortex automatically removes the colour cast of the light falling on an object before we become conscious of the colour.

In the early morning our visual cortex removes red and at midday it removes blue. What happens when we look at a photograph as there is no way of judging the colour of the light when it was taken? It seems some people are born to automatically remove red and some blue. One way of describing this is to say that some of us are midday people and some evening/early morning people. The visual cortex of midday people removes blue and so those people see the dress as white and gold but evening/early morning people remove red and so see the dress as blue and black.

28 February 2015