Most of the quilts at my guild have "blocked" backings, or have borders. There is nothing, these days, that says you have to have all the same fabric on the back. Quilters are getting creative with their quilt backs. I like it. More interest and always a surprise when using the quilt, more color, more movement. I don't see the problem, get a matching fabric and put a heavy border top/bottom or all four sides.
Diana