I used a simple stripe for the backside.
I found a blog that I love! She has the most beautiful combos of fabrics and lots of fun ideas. They aren't even all quilts so check it out even if you don't want to quilt.
But anyways, this is her tutorial that I used for this quilt. It was not difficult but very time consuming.
I love the way it already looks worn in with the raw edges on the circles!