It looks like he's going into shed, and the ReptiChip may have stained his belly (where the brownish spots are), I hear ReptiChip (or Grow!t, or both) stain easily in damp conditions. Doesn't look like an infection to me, though. As far as the dark black spots, it's possible it's just substrate, I see that occasionally in my snakes on EcoEarth, but it usually gets cleaned out on its own. Considering they went away on their own, I'm willing to bet that's what happened here.