Help: Chameleon colours

[Tony Brock]

I would really appreciate it if someone could explain to me exactly how 
a chameleon changes it's colors.

* Is there a movement of different pigments to the skin cells, or is each
  cell 'free standing' in that it has the ability to change to any color?
* What chemicals/reactions are involved?
* Is it controlled by the nervous system/electrical stimili?
* Has this been replicated in a 'man made' way, and if so how?

As you might have gathered from the potentially dumb questions I am a layman
in these matters, and would really appreciate some help.

Thanks.
Tony Brock       tours at iafrica.com