I had prewashed all my batiks for a warrior quilt but a red still bled when I steamed near it. Washed it in HOT water with synthrapol and all the dye magnets I had on hand (3), checked when it came out of the washer, repeated the Hot water synthrapol washing. Red totally gone from the white block and a hugh sign of relief from me because I needed to turn the quilt in the following week.
A quilting friend said she actually soaked a quilt in synthrapol overnight but that it did remove the errant color.
Worth a try and for me, nothing to loose, as I could not turn in the quilt with red bleeding onto a white block.