Thagrosh has always been one of my favorite warlocks. He plays very differently than most Legion warlocks, supporting both beasts and units about equally and being one of the few that can play the attrition game. Aside from his decent spell list and feat, Thagrosh can take care of business himself, which is always fun.
I painted him up the same as my other Ogryn, with the dark green skin that matches the beasts. Thagrosh also has a fair amount of gold on him to reflect his status as the bearer of Everblights anthanc. The fluff always talked about him having a skull like vissage, so I drilled out his eyes. I assume he just sees via the blight, a bit like Lylyth.