Do we all see the same colours?

Imagine the two of us, arm in arm, looking at a sunset, where the horizon is fretted with golden fire and the deep blue night encroaches from the opposite side of the sky. "What beautiful colours", I say, and you agree.

And then, in the space of the following silence, I am struck by a worry. I can point at the sky and say it is blue, and you will concur. But are you really seeing that blue the way I am seeing it? Perhaps you have just learnt to call what you see "blue", but in actual experience you are seeing nothing like the vivid, rich, blue I see. You are an imposter, calling my blue by the same name as yours, but not really seeing it the way I do. Or, even worse, perhaps I am the one seeing a pale imitation blue, while you see a blue that is infinitely richer and more splendid than mine.

Now I admit that this worry lies in the realm of philosophy, not neuroscience. You might even ask me why I am worrying about this when we could be enjoying the glorious sunset. But when you think about it, it is not clear that I could ever have direct access to what it is like to be you, and you could never have direct access to what it is like to be me, or someone else, or something else, such as a bat. My worry seems more plausible when you consider colour blindness, which affects around 8% of men and half of one pe.... Many people do not even realise they are colour blind. They live among the colour-seeing, getting by on the fact that there is usually some other difference between things of different colours that they can use to tell them apart, such as differences in shade or texture. [continue]