You know, I kind of like the idea of Koth as a painter. It hints to the players that he's not part of some dumb, marauding horde, but rather an organized collective with culture. Instead of a self-portrait, you could also have him be working a scene of Tiamat wreaking havoc on the land, killing humans, and doing all sorts of other terrible things, in order to give the impression that he is a religious fanatic (and linked to Tiamat), which is another big important clue to the players at this stage in the game. Also, I think it ties in nicely with Ulwai's opera, which maybe says something about the traits Azarr Kul favors in his commanders?