I have seen the black spot as well in deceased chams. I have no explaination for what causes it but it usually seems to be in a location that was bothering the chameleon before it passed. I have seen it near the kidneys on one with renal failure, in the stomach area in one that had just stopped eating for some reason, as well as top dead center of their head from an infection. None of mine exhibited the color except hours before passing, and they were all panthers and carpets.