If I have several large scraps, I will piece my backing, buying only what I need to complete the backing. If I have no scraps, I may use something very different on the back. The binding will match/blend with the pieced top and the back, but I love to turn the quilt over and find a surprise. If I want the backing to blend with the top, I take my top with me and spend time laying top and potential backings together in the store.