I read somewhere that one in ten people dream in black and white. I don't think there's much you could do to help it. You could try distorting reality:

This is currently my favorite reality check. Focus on something (a book, a corner of a wall, etc.) and really try to change it with your mind. You should be grunting, not blinking, and your face should give the impression that you are severely constipated. If you're awake, nothing will happen. If you are asleep, the object should distort and CHANGE COLOUR. Try doing it on a larger scale and focus on your dream world, trying to distort it and add colour with your mind.