If you don't want to use newsprint - old telephone books or even magazines, then I would suggest using a light weight muslin or any fabric that you might have on hand, preferably nothing too bright that would show through your strips, but any lightweight fabric would do. Personally I think I would use a white muslin for the middle diagonal strip about 2 - 2 1/2" wide, then add your strips to either side in any width your scraps dictate. I like the strip of white in the middle, as I think it makes the strips stand out more.