After getting the new appearance this morning, there seems to be two out of the three other tints available right now.
Winning ten rated battle grounds, doable enough, and the "Killing all Legion bosses" one. Now this one is not clear at all, who constitutes a "Legion boss"? Every dungeon boss ? Every raid boss ? Including ToS or not ? Do World bosses have to be killed as well ?
I'm looking for more information on the subject if somebody knows anything, or if there is a way in game to know.