A Resistance II skill could be made for each resistance color, Curse, Heat, Illusion, Cold, and Venom, and only players of that soul color could learn it. Since it would be soul-color specific, it would add a little more thought behind choosing which soul-color to create. It wouldn't have to be too strong of an increase, just a little something extra. I think it would be a nice distinction.
What do y'all think? Not trying to create more busy-work for Apoc, unless y'all think it's a good idea.