Re: FATE Core - what skill would include art?
I would definitely take from dnd3edm1's line of thinking. If the character's thing is a particular type of art, give them an Aspect relating to it. Then whenever it's important to them, invoke it for 1 FP and get +2 to the action. I doubt anyone's going to be able to provide much opposition to a Create Advantage roll based on dancing, painting, or an awesome guitar riff. If they need more than +2, then yeah, make it a Stunt. +2 to Craft when sculpting, or +2 to Rapport when playing music. Maybe +1 to Rapport or Provoke when playing appropriate music.
In general, if art is a hobby for them, then leave it as a hobby and don't put any real points into it. Even at +0, they're more skilled than anyone else who doesn't have professional training in it. If it's something they use for their adventuring, make it a Stunt. If it's important to the core of the character, make it an Aspect.
If it's something important to the whole of the game, then it should probably be made an Extra, and you could have an entire group of artists, maybe with their art having a character sheet of its own. A musician could have a few music-based Aspects, Skills, and Stunts dedicated to that. Painters could have the same, but specialized for what they're doing. Bronze Rule all the way, but only if that's the focus of the game.