That is beautiful! You could trace one of the butterflies to make a template and quilt butterflies all over it. Or flowers/loops/butterflies. I'd be tempted to use either a variegated thread in the blues or a gold (not necessarily metallic, maybe regular thread but gold color) over the center part and black in the border, just to add texture and not to take away from the center. Be sure to show it when you are done! I'd love to see that finished!