If after washing a completed quilt you still have bleed through use Zout. It's available in the detergent aisle. Trace the bleeding seam allowance with the Zout and re wash (gentle cycle is fine) and then dry.
How do I know? When doing a white and red quilt, the Hoffman red bled onto the white. I had pre washed and dried the fabric, too. The Zout worked! This experience has reconvinced me to always prewash my fabrics!