That's really lovely just as-is so i can imagine how it'll look once you put some color to it. My thought is that if you get very much color to the back-ground it could draw the eye from the center...I'm seeing the butterfly done in the variety of colors you have and the background done in a medium blue. For some reason, I feel that would create a nice balance while letting the butterfly keep center-stage. Seems like your piece could get too busy if very many different colors/elements are used in the background/border. Is that a laser-cut pattern?