Not all chameleons change colour in the way I think you are intending.
Whilst Panthers, Veileds and some of the other tropical tree-dwelling species can change to colours that include vivid blues, reds, yellows and greens, many species can only manage a change from dark to light colour.
Most leaf-litter dwelling chameleons have very limited colour changing ability - some don't change colour at all.
There are many theories as to why this is the case, and research is still being conducted on chameleons, but generally it seems to be related to the environment the chameleons live in.
The tropical tree-dwelling species seem to use colour changing more for communication than do other species, and this could be a reason for their wider palette of colours. There is a theory that vivid colours make it easier for chameleons to spot and identify one another in the dense forest canopies.
And leaf-litter dwelling chams, given their vulnerability on the ground, would probably never want to be spotted, hence they have developed more intricated leaf-like patterns on their skin, but have a reduced ability to change colours.
Even the leafs change to pretty bright colors when they are really pissed. These are old photos, and the light in the background doesn't help matters, but this little fellow was feeling a bit territorial. Take a look at his belly.. he was varying shades of yellow during that encounter. BTW.. I set up a second enclosure and moved the intimidated male along with some females.
I have a few other photos I will have to upload when I have time. Even the browns on them are pretty variable. There seems to be a slate gray variety of brev and a golden tan variety. roo has had red (bright tomato red) juveniles in the past, and I have a male right now that turns amazing shades of green and yellow. The brevs aren't as variable as a panther, obviously, but they still have their unique colorations. The males are more colorful than the females, and put on distinctive territorial displays to rival males, and also have brighter colors when they are trying to convince a female that they should breed. Their eye turrets turn very bright (whatever predominant color the male brev is) and get a black cross over them. I have seen males that fire up predominately yellow, others green, and one that is sort of a purplish red. Very pretty little fellows a lot of the time, and an entertaining species to watch all of the time.
The supers don't seem to change color a whole lot. They pretty much range from a very light tan.. almost white.. to dark brown and black when they are highly stressed. One individual animal that is owned by me but is currently residing with my vet (not because he is sick, because my vet "stole" him.. ) is more of a reddish brown than the others that I have seen. It isn't conclusive what species that animal is, though.
Eventually, I would like to move to some of the other leaf species. I like them so much.. they are really cool little animals. Each one seems to have a unique personality.