A fantastic hour-long podcast on the Perception of colours.
"To what extent is color a physical thing in the physical world, and to what extent is it created in our minds? We start with Sir Isaac Newton, who was so eager to solve this very mystery, he stuck a knife in his eye to pinpoint the answer. Then, we meet a sea creature that sees a rainbow way beyond anything humans can experience, and we track down a woman who we're pretty sure can see thousands (maybe even millions) more colors than the rest of us. And we end with an age-old question, that, it turns out, never even occurred to most humans until very recently: why is the sky blue?"
Thanks to Radiolab