How Many Different Colours Can We See?

We all know that some people see the world in a limited palette of hues due to colourblindness. But what's the largest number of colours that we can possibly see?

In this video, Sci Show takes us on a whistle-stop tour of colour vision, pointing out that normal folks can see about 1 million colours. But in fact there's a genetic mutation that allows a small number of people to register colours between red and green -- allowing them to see a staggering 100 million colours. Watch this video to find out how that can happen. [Sci Show]