No one's mentioned this yet, but it seems that for Evil Sims, when learning the painting skill, they will paint "evil" versions of paintings.  These tend to be darker and almost entirely in shades of red when at higher painting skill levels (around 5 or 6).  I have one Good Sim, and one Evil Sim both gaining painting skill:
Good Sim painted things like a bird, a father and son fishing, a clock, a cat lying next to a pile of books, and a scene from "Hey Diddle Diddle."
Evil Sim painted these same pictures, however the way the colors, shading, and lighting are make her paintings appear to be on fire.  She is now at level 10 and has the painting bonuses, yet will randomly either paint a normal picture or a reddish "evil" version.  Also, when first learning, her second picture was a red creature with horns; the Good Sim never painted anything like it.