On similar quilts I've either gone with a neutral, or with whatever color seemed predominant (usually matched my binding). Right now I'm using bright white on a Dr Seuss quilt so it will stand out a little but not be overpowering -- that thing is already crazy enough.
If you want the quilting to be featured, use a brighter color. If it's the texture you're after then pick something neutral. And if you aren't yet confident in your FMQ then don't pre-wash anything and let the quilt shrink up a bit in the dryer. It's a fabulous equalizer.
