I would quilt in the ditch around all the dark strips. Then.....if I wanted to add decorative quilting I would do a serpentine line of quilting in the center of the dark strips. I did some quilting in a sashing recently and used SCO-274 from The Stencil Co (www.quiltingstencils.com) I quilted this with the walking foot. Had to adjust the design so it would go around the corners but it worked great. The stencil has three wave lines so you can use two lines on the smaller and three lines on the larger. I had to go slow in order to keep the curves even but it worked out very well. Quilting this way only in the dark lines will give it some character. I am sure they (The Stencil Co folks) would tell you the distance between each line so you can get the size that would fit into the space.