without a pic its hard to tell, my xanth sometimes (temporarily) displays dark spots usually triggered by some sort of stress like occassionally coming into view of one of my other chams (2 are free ranging), sometimes she will display them after basking too close to the uv (rare), or some sort of displeasure with food, cage or other issues, she occassionally gets them when there has been too much activity in her area (like cage cleaning). they are usually only present for a day or two but they have hung around for a week or longer. my questions would be, are you fairly certain there aren't food, cage, activity, or other issues stressing him out ? if you have had it for four years, then what is your u/v (linear or cfl) and how long has it been since being replaced ? also you mentioned 70f , does he have some sort of uva / heat basking available? also what is basking distance and schedule ? (just a hunch, but i suspect its somehow u/v related) i dont know your location but, if weather permits, you might try getting him outside on a sunny day (above 50f) for an hr or so (out of his cage) and see what happens. you might also want to review your supplemental regimen to see if maybe there is some sort of deficiency or excess (long term slow build up) of something? not all will agree, but in my opinion, older chams often dont need as much supplementation. / although they can live significantly longer, 4 years is considered fairly old as far as captive jackson's go, so you must be doing something right. my suggestions would be review the forementioned items for starters, also you might want to weigh him every 2 weeks or so to make sure he is not losing weight, it wouldnt hurt to look at the spots with a viewer or magnifying glass,(this also helps to confirm or deny the presence of mites as a cause) also you might try lightly pinching one of the spots and gently pulling it away from its body to see how elastic the tissue is (necrotic tissue is not elastic, like healthy tissue) if the tissue is not necrotic, his weight is stable and his feces looks and smells healthy, my guess is he is probably ok, it might just be a sign of the onset of his twilight years . but, if you are able to afford it, a CHAM VET visit is probably in order.