I can't remember where but I read the best explanation of when to use color catchers that I have ever found. Dye and how to stop it has to do with chemistry (acid or not) and how the fabric was died. Basically if it is a dye that sits on top of the fabric (do you get it on your hands if you rub it) use a color catcher because of how it reacts with the dyes and the kind of dyes that are used in that process. If the fabric color doesn't rub off on your hands but runs in water then use Retayne. I wish I could remember where I read it.