Hmmm..... tossing an idea out.... what if the basic necromancer had a 3/4 sleeve robe with the belt and pouches and necklace. Then, and as it levelled up, the robe might be ragged in places, stained with blood or burned or torn, and as it continues to level, there more exposure and less concern with normal mortal clothing, leading to a slightly rag-ish appearance and more accessories, more carved bones or tattoos or more bits on the staff or the skull around it's neck having a faint glow now and then. The final level or two could be a lich-type appearance of wasted/partially ephermal. Sorcerers go for the arcane cocktail party suave presentation, necromancers get their hands dirty and are willing to muck in any messy ritual or drink/eat anything at least once. Wouldn't be bad if they were attracted to new corpses for a short while of musing, or hung out at the prison to watch mortals waste away...
http://melaniemaier.deviantart.com/art/The-Undead-Warlock-342498254
http://mattdonnici.deviantart.com/art/Lich-296149433
http://namesjames.deviantart.com/art/Graven-Lich-MtG-279736197
http://melaniemaier.deviantart.com/art/The-Undead-Warlock-342498254
http://mattdonnici.deviantart.com/art/Lich-296149433
http://namesjames.deviantart.com/art/Graven-Lich-MtG-279736197