The scenario sounds fun. I'd ask the players what they want to paint, and make three checks (Int/Wis/Cha) to determine the result:
[sblock=Spoiler
Creation
Int for detail or novelty.
Wis for emotion and purpose.
Cha for accessibility.
Examples
Int (low): "crude," "simple," "crafted with so little care," "a child could do it," "tired," "common," etc.
Int (high): "intricate," "made to look easy," "absorbing details," "never before seen," "invented a new technique," etc.
Wis (low): "no heart," "aimless," "nothing to say," "a faint voice," etc.
Wis (high): "stirring," "courageous," "never before have I wished for tears to shed..."
Cha (low): "only a few viewers would understand," "presented in such an obtuse way," "a mother would avert her children's eyes," etc.
Cha (high): "conveyed so precisely," "easy to grasp," "art for the masses," etc.
(Int-, Wis+, Cha+): simple colors and strokes belie a clear and poignant heart.
(Int-, Wis+, Cha-): a beautiful message lost in a distracting mess of chicken scratch.
(Int+, Wis-, Cha+): a simple message for simple masses saved by utterly transcendent craft.
(Int+, Wis+, Cha-): magnificent skill and meaning defeated by offensive content.
An intellectual critic might prioritize craft (Int), an empath might prioritize emotion (Wis), and an outcast might prioritize art that defies "common" sensibilities (Cha).[/sblock]