Retayne and sythropol are two different products.
Synthropol will keep excess dye in the wash cycle from settling or bonding to other fabrics. It is typically used once fabric has been put into a project. Synthropol does not neccessarily keep colors from running in future washes. It does not solve the problem of excess dye that may still be in the quilt and the wet quilt is sitting in the washer having finshed its full cycle, and the moisture will still allow for excess dye to migrate to the surrounding fabrics. Products washed in Sythropol must be washed in warm water in the next washings ( according to the label).
Retayne is a fixative and will prevent running or bleeding prior to construction. Fabrics treated with Retayne must be washed in cold water ( According to the lable).
I have looked for both at JoAnns and never found it. I get it at my local quilt shop.