I believe that there should be a way to flood-fill uncolored areas of elements on the decoration editor. I think I know how I could make it work. Since the uncolored elements are all the same color, you could make it so it senses whether it is the color of one of the elements, lets say dmnd, and it colors all the elements that color whatever color you have chosen.

One Drawback:
It would not be able to work if you're coloring something else the exact color of the element, except you could place a line of another color to stop it from coloring the one you want to be that color.

Any feedback helps and is appreciated.