Hello,
Brumation is Underwater...those I've kept at the Bx Zoo, over many years, have remained active when kept warm. However, others do slow down even if warm.
If the skin is an unusual color, best to check all water quality parameters and do a water change...however, I've not known them to leave the water even when ammonia levels were high. However, very high levels do cause skin irritation/discoloration in amphibs, some softshells; alligator snapper skin may be sensitive in this regard. Some species will leave if water is too cool (or obviously, too warm) but this is rare. Wild individuals bask in order to drive off leeches; they also leave the water due to aggression or when seeking a nest site. Other aquatic species will bask when afflicted by skin problems - fungi, etc. Let me know if you need help in locating a vet, in order to check for skin problems. You might enjoy - The alligator snapper pictured in
this article of mine is 205 lbs, the common snapper (top photo) is 70+ lbs. Best, Frank