The way we perceive colour depends not only on an object's pigmentation but also on our preconception of what the object is supposed to look like, according to researchers in Germany.
Karl Gegenfurtner and colleagues at the Justus-Liebig-University Giessen asked observers to alter colour information in images of fruit and vegetables so as to make them appear black and white.
Subjects adjusted the image of a banana to be slightly blue, suggesting they were compensating for a perception that banana was yellow. Similarly, they adjusted a lettuce so that it was slightly red.
The results, presented in the November issue of Nature Neuroscience, suggest that our perception of colour is a product of actual sensory data and the brain's expectations of what an object's colour should be.