If you noticed, Pollux's extremities are black. This is part of his demon biology, in which the more emotionally intense (re: madder) he gets, the darker his skin becomes, with the black creeping up from extremities to the rest of his body. At a fully enraged state, what were originally his dark extremities will begin to glow a molten yellow color. It's hot, yes.

The same could happen to Castor but he's almost too laid back to get mad at anything.

By  NaughtyImp