Here are some random magic + art ideas:

Magic Medium- Enchantments upon paints, pigments, chalks, and such that have their various effects on finished works. these would include:

Planetary pigments that only show the entire work when the moons and stars are right.
Racial pigments only a certain race can see allowing 'hidden' subject matter.
Guild pigments that allow art to do any number of things for guildmembers that view them.
Recall pigments that bards would appreciate.
Holy pigments that stir the spirit when viewed.
Holy pigments that allow a piece of art to sanctify a room for a time.
3-D pigments that become the view they portray allowing the viewer to enter or leave the image as they would a room and viewers outside would see a still of who was in the artwork.
Prison pigments that would encase a viewer in the artwork for a time.
Construct pigments that become paper constructs of what you draw.
Mana pigment allows a piece of art to alter the mana in any room it is placed similar to nimiero stones.
Chakrel pigments for those hard to please barbarians.

Just a few of many ideas .. hope this sparks something for someone.