I have a reason for preferring white on some of my quilts. A dark backing will show through if you have white background in your quilt top.
Mom has told me about using muslin because it was cheaper. But the 1850's quilts she has, that were made by her great grandmothers, were backed by prints. I do not know of any 'law' that decrees the backing you should use.
All in all, I would say do what you want to do. You have your own reasons for the fabric you use.