I agree with Rose. But instead of stitching in the ditch throughout quilt, I'd start in center to "tack" a small section. Then near the outside; where the strips are, stitch in the ditch there. On both sides.
Most people are going to look at the back of the table runner, and it can be reversed occasionally. I'd go with any solid color for the backing. Brighter is more pleasant I have found.
Incidentally, you did a great job on the quilt and it is beautiful!
Stephanie