If you have a piece of fabric that is bleeding, you would use Retayne to set the dye. You would not use Retayne in a load with several different colors.
If you want to wash a quilt and are afraid something might bleed, wash in Synthrapol. Synthrapol will suspend unset dye particles in water so they can be rinsed away instead of settling into other fabrics. I don't prewash my fabrics, so I always wash a new quilt in Synthrapol. (I do test fabrics I suspect might be "bleeders".)
You would never want to wash a quilt in Retayne because it could permanently set a bleed into other fabrics.
Just be aware that Synthrapol may not be able to handle a red (or other color) fabric that is bleeding copiously. There's only so much it can do. If you suspect a fabric might be a heavy bleeder, test it before putting it into a quilt, and wash it in Retayne if it bleeds so that the dye is set.
Someone on this forum had made a Christmas tree skirt. Her husband accidentally spilled water on it and the red fabric bled into the white. Even with Synthrapol, she was not able to change the white fabric back from being dyed pink.
Synthrapol can sometimes remove existing bleeds from a quilt or an embroidery piece but that is more iffy.