Retayne sets unset dye; however, it is typically used on fabric yardage before the fabric is cut for piecing. This is because any bleeds into other fabrics will be permanently set.
The usual treatment for a quilt top like yours is to wash the finished quilt with Synthrapol. Synthrapol is designed to suspend unset dye particles in water so they can be rinsed away instead of settling into other fabrics. For this you need to use hot water and the biggest washing machine you can find -- so there is lots of water for the unset dye to stay suspended. You can also toss in lots of color catchers (in lingerie bags so they don't shred).
Vinegar and salt set some types of organic dyes; however, almost all dyes used now commercially are chemical dyes which require chemical setting agents.
Your bleeding fabric is most likely one that is over-saturated with dye (more dye than the fabric fibers can absorb). A few washings with Synthrapol are likely to take care of this problem.
Less common, although it still happens, is a dye that has not been properly set in the factory. This type of fabric can continue to bleed with every washing unless the dye is permanently set with Retayne. Some fabrics require two treatments with Retayne.