Once you sew the contrast onto the binding, the only thing that is different is that the binding is stitched onto the back first. Everything else is done as usual--miter the corners, and when it comes time to stitch the two ends together, just use whatever method works best for you. Just be sure to match the contrast so it is straight across. Before sewing ends together, pin to check placement of contrast. To keep it from shifting, either use a few hand basting stitches or use Elmer's Washable School Glue (a little in the seam allowance close to the stitching line--don't forget to press where you have glue to set it).
Pat--"Keep Calm and Carry On"