The only reason we don't see in black and white is because the way that color reflects/hits objects...
In dreams, there IS NO LIGHT BEHIND OUR EYELIDS, therefore we cannot, in essense, 'dream in color'.
*The only reason why we dream in color is because of MEMORY*
Now...relate this to blind people....they will dream using memories of SOUNDS mostly, flashes of hypnogogic imagery, etc...mostly the other 4 senses....