Hey guys!
This is a suggestion thread on the forums for Fel-orcs to be brought into the fold — Whether it’s via a questline or otherwise towards giving some oomph to our already existing race of orcs (OG) through additional cosmetics @ the barbershop. 
The Fel-Orcs
We have already seen a friendly fel-orc quartermaster by the Dark Portal from many years ago – Whether they were a modeling mistake or a genuine design is up for debate, however given we now have the Man’ari fighting alongside the Alliance — I’d hardly wager us having friendly fel-orcs as “out-of-the-question” for our orcs to have stand alongside them once more.
- We already know of the original designs of the simple redneck orcs in Outland, some of which who had even served Illidan in the past. However we also have the OTHER variation of Fel-orcs, of which we saw in Warlords of Draenor and later some more in Legion.
I’d wager the later variations were due to Mannaroth dying and having to utilise another powerful demon’s blood for the shadowy / fel empowerment – or still using the dead-demon’s blood, and empowering it with fel-magics so it’ll still have an effect - but they just wouldn’t be bound by the same blood curse that the original ones had (Hence why Sean Copeland had originally stated they’re not necessarily true ‘fel orcs’ of sorts, but more-so just fel-empowered).
Fel Orc Variations:
This brings me to the idea of three prime customisation options for Fel Orcs:
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- Gluttony of Outland’s Fel-Potential: Simple Red Skin, etc
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- Ameliorated Fel-Gift: Fel-marked gray, green or blackened skin with horn-like growths, glowing green or red eyes, and glowing green “cracks” on the skin along with glowing green hands.
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- Masked Fel-Strength: Looking like ordinary green orcs, but when enraged or under lust-effects … Red skin & glowing eyes triggers (akin to a second form, like Dracthyr or Worgen have).
Aside from red for masked fel-strength, you could also have ORANGE via augmented Fel-Power with earie golden glowing eyes, flame-hued veins shown on muscles & glowing horn-like growths.
Detailed Explanation -
(1) The first one is token–nod to the ones we see in Outland.
(2) The second was inspired from the WoD / Legion fel-orcs.
(3) The third was inspired from Grommash Hellscream (original) when his skin turned red with with glowing eyes after drinking the demon-blood for a second time and entering a blood haze as he battled & killed Cenarius 
The added suggestion towards the option of orange-skin was derived from Gul’dan (AU), as he had transformed when his fel-strength was augmented by the tremendous power of the Nightwell.
Questlines & Lore:
You could present a similar ordeal with the Man’ari with the Fel-Orcs, however I think it would be best if we had a few story-lines for each variation of the three fel-orcs. Emphasising the different journeys, lore and giving a respectable nod to the world-building that’s been established overtime.
- Naturally with the first variant – You could argue they were simply corrupted by the fel-influences around them in Outland had effected them, alternatively you could also suggest they were simply the Horde’s spies of the Shattered-Hand in Outland who were forced to drink the demon-blood in order to fit-in … Additionally you could wager they served alongside Illidan & his demon-hunters to ultimately stop the Legion.
- As for the second – You could wager you were part of the Bleeding Hollow Clan who did not like what had become of their home-region under Gul’dan & thus rebelled – or that you were a Shadow Council orc who had redeemed themselves by turning coat & using the attained powers against them; or simply that you woke up the next day and realised that darn hunchback orc spiked the punch-bowl.
- The third you can be fairly clever with, you can use either of the above two — or that you simply drank in fel power, demon blood or other dark powers into your being and managed to master & mask the attained powers within.
Naturally these are suggestions, and can be changed or presented to where it’s ultimately up for interpretation & wide-scoped roleplay.
Ultimately:
I’d love if there could be a surprisingly heroic or redeemable aspect to the lore of them and that they’re NOT just yet another sorry-fest of guilt-riddled wrong doers who flipped very recently and begged to be forgiven & accepted …
Anyway, there you have it guys!
I hope most of you have enjoyed the thread, if you have any great suggestions to add, or any intriguing thoughts to share – Feel free to comment bellow! 
You could perhaps wager it was them who severed various portal conduits in Outland and disrupted signals in the nether to prevent as many warlocks, fel-infused beings and demons of the Legion from invading Azeroth – indicating it could had been far worse.