I think quilters get stuck with the feeling they have to "match" everything. I find that if I just try to get something that "coodinates" instead, I have better luck. If I like it and it blends well, and it goes with the binding, then it will look fine. Sometimes the coordination is color family, sometimes style of the print. I usually piece my backings with decorative touches, such as a row of blocks or strips from the front. It enlarges the backing and adds some interest to it.