magic might vs infernal

(serfs parma)
When a magical creature "turns to the dark side," if you will, does it's magic might become infernal might? Does it's vis become tainted by the infernal?

There is no set rule, it's the kind of things you have to decide on a creature-by-creature basis. But both are indeed plausible, yes: a creature can be "evil" without turning infernal, but if it does (which can happen - witness, Infernal ghosts), its vis is likely to become tainted.

Yup, I beleive there's a hint of something like this in RoP: The Infernal.