If it was me, I think I would grab the multi-colored polka dot on black fabric that I love so much.
You have a few that are reading as white in this picture, so I would go with Black. However I would agree and use a wild print that contains most of your solids in it!
I agree black would be good. How about black with tiny white polka dots!!
I love your bright colors, Black would make it have an amish flare. Or a back with stars or poka-dots would also be neat
I think a black/gray semisolid print would look great. Something dark, and not necessarily with any pattern, but with color variations.
Black would be beautiful! I love your fabric choices!