I would take the quilt to a fabric store and try it against dark blue and dark gray solids and plaids (flannel if you can find the right colors). You don't show the back of the quilt. You would need to add a border piece to the back that works with the backing color.
It would probably be best to sew one border on at a time. For example, right side top only first, easing top to fit measurement of border, then turn over and add backing border along the same line of stitching.