I have had success with Retayne but it is work. I bought an aluminum roasting pan and cooked like colors per directions and then let it dry. I have a front load washer so I didn't think that method would work.
Use Retayne when you pre-wash the fabrics to help set the dyes. Do NOT use it on a completed quilt, as it will fix any dyes that have migrated to the other fabrics and you'll never get them out.
After you've completed the quilt, use another product called Synthrapol. This keeps any dye that gets into the water from settling on other fabrics.