The world is full of colour! But, listener Maya Crocombe wonders ‘how do we see colour and why are some people colour blind?’

Dr Rutherford and professor Fry set out to understand how special light-sensitive cells in our eyes start the process of colour perception, why people sometimes have very different experiences of colour and whether, in the end, colour is really just ‘in our heads’.

Dr Gabriele Jordan from Newcastle University explains why lots of men struggle to discriminate between certain colours and why there were lots of complaints from colour-blind viewers when Wales played Ireland at rugby.

Professor Anya Hurlbert, also from Newcastle University, tackles the most divisive of internet images: The Dress! Did you see it as blue-black or yellow-gold? Anya explains why people see it so differently, and why our ability to compensate for available light is so useful.

To see the Dunstanborough Castle illusion as described in the episode, check out the Gallery on this page and also on the Discovery homepage.