Your quilt is really cute. All sorts of combinations would look nice. I would want a color matching the background in the squares to not take away from the cute appliques but I would want the quilting to stand out on the border which appears to be a solid or near solid. So, I would go light or varigated light for whatever motif you choose. If you haven't chosen your backing I would go with something light so as to accommodate matching thread on top and bobbin. We would like to see the finish.