Up and down arrows to change the pen color. Left and right to change pen size. Space to replay your drawing. X to clear. Z to delete last layer (some glitches may happen, I'm fixing that).
All code by me. Updates: v1.0 (Basic features) v1.1 (color and pen size added!!) v1.2 (layers..) v1.3 (save/load drawings) V1.31 (fixed a data corruption error)