Re: what is in a lizard's body to allow it to change colors?

Lizards, along with some crustaceans and squids and octopuses, have large 
branching cells called chromatophores within the skin. These cells contain 
pigments (colored molecules) that may be concentrated in the center of the 
cell, where they are almost invisible, or can be dispersed into the 
branches when color change is desired. This process allows a fairly rapid 
change in skin color. Chameleons, which have the most advanced color-change 
ability among the lizards, have two different layers of chromatophores in 
the skin. One layer contains red pigment, the other yellow. Another deeper 
layer reflects the colors in the chromatophores.

For a good explanation of chameleon skin color changes see this website: http://www.pbs.org/edens/madagascar/creature3.htm