Chameleons changing color in order to match their background for camouflage is a complete myth. They change color according to their emotional states and if they happen to match their background in the process, it is an utter coincidence.

The following things can make a chameleon change color:

-Fear
-Light
-Temperature
-Heat/Attracting opposite sex
-When handled
-Aggression/Anger (after fight)

The skin is covered in several layers of specialized skin cells called Chromataphores, each cell containing a different colored pigment.

Chameleons can rotate and focus either eye entirely separately to look in two different directions at the same time but they are completely deaf.