YA novel about a world where art, music, etc is totally forbidden. The story follows a pair of twins who are separated in their youth because one draws a picture in the dirt, I think the other twin reported their brother to the authorities? The artistic twin is saved from death/punishment by a resistance (i think) and lives in a safe, magical world. The story follows the twins as they grow up and train for the day when the artistic world will be attacked by the unartistic. At some point they realize the other is alive (i think they both assume eachother to have died?) and impersonate them.