I tend to back a lot of my quilts in muslim but if I am putting a fabric other than muslim on the back I like them to at least coordinate. Of course I am also the person who can only do organized scrappy quilts. The ones with brights and earth tones and primary colors and pastels all mixed together set my teeth on edge. Bottom line quilting is an art form and in art it is what the artist sees. So I do agree your quilt, your rules unless you are making a commissioned quilt.