I made a double sided quilt just over a year ago. The front was an assortment of stars done Amish fashion and the back was a plain black.
I used Japanese quilting in grey which was a neutral for the front. It looked fantastic and really gave the plain side a real oomph whilst the colours just stood out on the patterned side.
Hope that helps. Will look to see if I have any photos of it so I can post them.