She wore black when she was part of the Dark X-men.
That's true. But that was very brief and had the in-story reason of (IIRC) wanting to disassociate from the actual X-Men while being on Osborn's team. @ApatheticAvenger said:
So Mags shaved his head huh?
Whoa, I didn't notice that until you pointed it out. Seeing Mags without his giant tuft of white hair feels very weird.