Hi, here pogona-vitticeps.Ch (maybe the filmclips that show how pets should be able to live and what can happen in extraordinary cases* will help you) .
*extraord. Cases: a bd got out too early from the egg. And other is case of black beard...
I wonder, when this was posted, as i dont see any answer. And after 4 years only you notice this? I can see the same now, after 2 yrs. As my pets have never been ill and are very lively (see filmclips) i think that the parts you believe are like painted in fact are the normal skin when he is erected or just angry. And the light parts might be old skin, shortly before falling off. If you put him some jojoba-oil or just high qual. Olive oil to help the skin renew, or even just a warm bath will help, you will see if it is something else. If it is a mushroom (yeast or candida-mycosis) infection, please let me know.
You can therefore also add some teatree oil, but just like 1 drop aeth. Oil on 50 ml (half dl) of simple oil and rub it in. Or neem oil, available already in mixtures to be added to the skin. Both can be swallowed and therefore is not a danger for them (i hope, you dont hold one animal alone in a kind of "einzelhaft" which is highest punishment in prison - single cell capture. Else i wish you the same.. All the best