Actually, you are misinterpreting the meaning of "bright" color. Color change is triggered by stress, both good and bad. Your chams are stimulated by being out of their territory and by being handled by a large odd-looking intruder. They may not be horribly upset by it, but bright color doesn't really mean "like it". We know that some chams tolerate handling better than others. I'd say your chams are reacting to the handling by getting more aware, excited, and possibly feeling a moderate level of stress. If your cham was totally cool about it they wouldn't change color much at all.