Colour, always. Even when I was a young child, I have never had a black & white dream... Though I did have a sepia toned one because the dream took place in the early 1900's!
I'm not sure if anyone ACTUALLY dreams in colour, as it's been speculated that our minds trick us into believing the colours are actually there... It's probably just a matter of imagination or vivid photographic recall, since no one's eyes are involved at all in the dreaming process, which is where one usually receives colour input.