I don't know about what Eddo said, but I do know that normal red hair is a mutation of the gene that causes black hair, and is the reason why it's pretty much impossible at this point in time to make a proper red hair dye...that actually looks like natural hair.
My hair's a mid brown with golden highlights, and if I get in the sun or a brightly lit room it looks like I have a halo. A big fluffy, shaggy halo.