So we've gotten the confirmation that the Warlock-only quest line in 5.2 will indeed give us green fire (FINALLY!), but here's another thought I had about it:
Since the green fire will be most enjoyed by Destruction Warlocks, wouldn't it make sense to also have the Codex of Xerrath affect the color of the fire that surrounds the Warlock as embers build up? Maybe also change the default UI of the ember bar to also show green embers instead of orange?
It wouldn't make very much sense to be engulfed in orange flames, but be spitting out green ones, now would it?