"At the warfront all the NPCs that are night elves actually have the darkened eyes. So theres definitely a sense that in proximity, fighting on behalf of the dark element of elune, under the darkened moon, thats what happens. (…) “But I think in the story sense, that any night elf that is fighting on behalf of Elune in that confrontation, their eyes would be darkening” - From the recent lore Q&A
“Elune has the power to do this. We’ve established that she does. And here it is again. She calls upon it. The unnatural dark falls upon Darkshore. And it gives the Night Elves a battle, you know, enhancement. Right?” - 55:22 Terran Gregory interview`https://www.youtube.com/watch?v=aEHc8le_Qpk´
“It’s very much Sentinel and Warden inspired. Right? And Wardens are, as we know, the keepers of vengeance. And while they were crated very specifically they’re still, you know, at their core a Night Elf institution. The concept of wielding vengeance as a weapon. And I felt that actually factored into this. This was just my feeling in putting this story together. If they are capable of being empowered by vengeance, then that means they’re more powerful after they lost Teldrassil than they were during the fight of Teldrassil.” - around 58 min
The night elves during the Alliance assaults and in Boralus all KEPT their black eyes.
So this tells us several things on how a night elf gets the black eyes:
- Be in Darkshore
- The night elf in question needs to have faith in Elune (you fight on her behalf)
- More specifically, he/she fights on BEHALF of the DARK ELEMENT of Elune → IMO this suggests you need to be vengeful and determined to destroy the Horde.
→ So far it seems like the black eyes are tied to the eclipse and the dark element of Elune. Chances are high it is not permanent.
Does the blessing remain outside of Darkshore?
Judging by the in-game Sentinels in Boralus and the Alliance assaults, they definitely stay when outside of Darkshore.
Can a character fight in Darkshore but keep the normal eyes?
I believe a character that does not embody the traits of the DARK ELEMENT or lost his/her faith in Elune would not receive that blessing despite fighting in Darkshore (judging by the sources above).
What powers does the blessing grant?
The blessing seems to be inspired by the Wardens who are known to wield vengeance as a weapon. It’s quite clear it empowers them. After Tyrande completes the ritual, the player (and the NPCs) receive a 30% buff on HP, damage and mana regeneration. This is in line with what was said above: It is a general battle enhancement, that one could easily translate into different aspects in roleplay. Perhaps your character is stronger, faster, more determined and with a goal in mind (can fight longer?). There’s unlimited freedom there, tbh.
What about Shandris, Jarod, Malfurion and Mordent?
They seem to have unique models. Chances are high Blizzard simply was too lazy to update them (seeing as the black eyed elves are pretty much all copy-pasted). Anything Malfurion related I would not take so serious. Man is the only druid that who has emerald eyes and he is -the- Archdruid.
Another possiblity is that they simply do not share the same intense feelings of vengeance as their comrades. Shandris and Jarod in specific seem quite level-headed in general. Mordent as well (we don’t know about his faith either). But that is of course speculation.