The principle as I understand it is that color catchers attract the "loose dye" that has not been "set" in the dying process. They will work repeatedly until all of the loose dye is caught. Retayne is a chemical dye setting process. Usually only one Retayne procedure is necessary if instructions are followed (amount of Retayne, water temperature, length of soaking). The advantage of the color catcher is the ease of use, especially after the quilt has been made. The disadvantage is that you can lose color. The advantage of Retayne is that you have actually "set" the dye.
I have only had one experience where something treated with Retayne bled in the rinse water. I actually did two treatments and still no success. It was a black piece of fabric from an unknown source, and the sides of the sink ended up with a waxy black coating. I have no idea what kind of dye was originally used, but that piece of fabric became a donation to the local community theatre group to use as draping.
Always pre-washing,
Dayle