Light meditations for healing etc.

[Milamber]

I bought a CD about 4 years ago, it had some music that was soothing and some guy walking me through meditations on it. I dont have it anymore, it was called brain-something...cant remember. So anyways one of the meditations included imagining white light comming into the body and entering the cells, energizing them. Another involved purple light entering the brain and entering the brain cells.
I am a firm believer in visualization. What I would like to know, is there any significance in what colors you imagine when doing these types of meditation? Why purple for the brain? Would blue-white light work for healing, what about red, green, etc? Perhaps someone knows something about the colors and what they mean...?