Love this take on the concept. I had a fleeting "what about musical scales" when I was thinking of ideas but quickly discarded it because I am not a musical person. I also think the art style while simple is quite effective and well done. I always appreciate a game jam game that manages to look "complete" for lack of a better word, so well done!
My only complaint is I'd love an undo/redo button, the command programming pattern could do wonders for this game!