Re: molecule changes:chameleons vs photochromic produc

That's a good question. What a chameleon does isn't quite the same as the 
thermal changes of "mood rings" and the stuff like that.  A chameleon, like an 
octopus, has a lot of differently pigmented cells that open or close to reveal 
or conceal their color, making the creature appear to change color, or aquire a 
particular color pattern. Another variation in the animal world is 
"piloerection", where the animal (like some rabbits) has two colors of fur, and 
raises or lowers particular hairs, making it appear to change color. Then there 
are some, like the artic hare, that actually change which color fur they grow 
depending on the season. The thermochromic pigments stay visible, but the 
wavelength they emit changes depending on the temperature of the pigment; some 
other pigments are sensitive to pH, like litmus paper. So actually the two 
(animal color change and color-changing plastic) don't really have much in 
common.