Colour Changers

Sometimes black is not black, and grey is not grey. I'm not sure why, but it's like that.

I walk into a store and buy a pair of pants in black. I'm at home trying them out again and matching them with my other clothes, and everything is great. But the first time I wear them outdoors (in the sun), they magically appear to have a red / green / blue tinge to them. And suddenly black isn't black -- it's super-dark-green.

Now try matching them to another "black", which seems super-dark-red now in comparison. Even from the same brand of clothing. Why do they do this to us???