Originally Posted by Manic
I've read an explanation for that. Originally, Northstar was intended to have pure black hair, but many early artists used streaks of white in his hair to indicate how much sheen it has. Later artists would interpret the white streaks as grey hair instead of lighting effects, and thus Northstar is sometimes drawn with grey hair instead of black.
It's the same reason some artists can't decide whether the original X-Men costume was yellow/black or yellow/blue.
Isn't that what also happened with Jim Lee's Storm costume? Wasn't it supposed to be all black with white streaks to indicate sheen only to be misinterpreted as being white?