You’re being awfully hostile over Void Elves discovering hair dye, my guy. I’m saying we should not give them any excuse to renege on adding new stuff, no matter what it is, so long as it lines up with lore. Blizzard abandons things at the drop of a hat, especially customization.
Allied races were already a way for them to take what they’d made for primary races and slap it together to make more money and burn more player time. You think if they decide to not give the hair colours to the Void Elves that they’ll magically decide to use those resources for Blood Elves? Hell no, they’ll do (or allow, I guess, since the art team likely wants to do more) the barest minimum and that will be it.