your friend is obviously a complete arse. red is a colour, therefore to have to explain what colour a colour is, is completely nonsensical. it's not deep, it's just pretentious.
hey man, how green is green?
You're friend isn't on drugs, nor is it a daft question. 'Red' is several different shades, but if you were a dog for instance wouldn't exist (because they only see in black or white and they have no such thing as red). Red and all other colours aren't physically 'there', they are just something you percieve.