They are used differently. Retayne is used to 'set' the dye into the fabric to help prevent future bleeding. Color catchers simply help collect the loose dye that comes out into themselves so the excess dye does not collect in your other fabrics. If it was me, and I had both on hand, I would first wash with the Retayne following the directions on the bottle regarding water temps, etc, then wash a second time with the color catchers to see if they come out clean. If so, you should be good to go. On the other hand, if you only have color catchers, wash once and see how discolored the catcher is, and if it has picked up lots of dye, wash again until your catcher stays white, meaning no more loose dye came out.