Please don't use white thread on this beautiful quilt! I would first SITD (every stinking seam, to quote Cindy Needham) and then determine whether the quilt needed more quilting. If so, I think I would stick to straight line stitching, either using black or matching the thread to the patches being quilted. Normally I would try to introduce curved lines to offset the strong lines of the design, but in this case I think more straight lines would be ideal.