Now now, we shouldn't conflate the actions of Thancred and Best Ascian. Best Ascian is Best Ascian and Thancred is . . .not.
Though more seriously, where in the west black tends to signify death (consider: funeral colors), it's the opposite in Japan, where white does (corpses are dressed in white). That may have something to do with it, since we usually have dark haired villains. Or it could be that white hair is simply more popular in Japan due to more characters in media having it.