Don't wash it until it is quilted. I don't prewash fabrics. Instead I take my finished quilt to the laundromat and wash it using Synthrapol in their largest front-loader. The large front-loader uses plenty of water to dilute any dye bleeds, and the Synthrapol suspends any loose dye particles so they dont' have a chance to settle into other fabrics. The key to this working well is to use a *lot* of water and Synthrapol in the water.
Do ***NOT*** use Retayne on a finished quilt! Retayne will permanently set any dye bleeds. Retayne is what you use on a bleeder fabric to get the bleeding to stop.