@Zanna(View Post) color picker: use the middle mouse button over the element to sample it, or if you're in the decorator, to get the color. Undo: hit ctrl-z, doesn't work in decoration layer though. I don't think fill or cover is possible, and it has been suggested before.
I didn't know about the middle mouse color picker! Thanks so much for telling me! I always thought that would need to be added to the game, I guess not now! :)