When basking they do turn darker in colour to absorb the heat. Similarly, if they get too hot they will get much lighter in colour and sit with their mouths open.
I think that it also happens because you have taken the chameleon out of its safety sone/territory and its affected by having to be "on guard" for predators.
Seriously...I half way understand not using the search as I know it's some what more fun to start a new thread...but when the same thing is being discussed on the same page in the same forum. Come on, are you serious.