Beardeds color up or down according to their moods and stress levels. Ever hear the expression, "when fired up"? When they are angry or stressed they are darker, and have dark striations on their bellies. When they are happy and there is little stress they brighten up from their normal color. I don't think that this ability is intended to help keep them from predation (camoflauge), but more for socialization/interaction with other dragons.