I like picking a busy fabric for the back that has at least some of the colors from the front incorporated. Busy fabrics help hide quilting mistakes. Sometimes I will pick the reverse of the front. I did one quilt that was pink & white with little appliqued doll dresses on the front. On the back, I found a multiethnic matruska doll fabric with a black background. It looked absolutely beautiful & was easy to seam down the middle due to the repeating pattern.
The quilt I designed myself has a seascape scene, so on the back I am seaming together 3 fabrics -- RK Ocean, RK Atmosphere & a solid teal fabric to match the teal line that runs down the left margin of both. It mimics the front both in color scheme & with the bubbles since I am appliqueing bubbles on to the front. I always think it's nice when you can carry a theme to the back of a quilt, but that's just my very humble opinion.
It might be fun to pick a bright colored fabric for your back since you did black and white on the front.