White and blond hair colors are not unique for blood elves in any way. In fact, from all playable races, void elves are ONLY race who don't have white hair option. Alleria have blonde hair, so I would not restrict void elves to that color either. Blood elves also got blue hair color tones, which is something what was void elf thing before (well, different tones, but still blue).
I also don't think hair colors are the most optimal options for maintaining unique feature of the race. I'd rather see blood elves getting runic tattoos and similar stuff and void elves getting something different for these races having different flavors.
On the other hand, if there have to be some differences in hair colors, I think brown and red color tones are the best candidates to remain on blood elves only.