"Tint Color Map
By putting a map in the Custom slot and checking Use Tint Color Map you can have multicoloured tinting.
This is only really useful for stained glass and the like, which is a fairly rare case but is necessary from time to time.
It's probably advisable to not use this in conjunction with a Tint/Cloudiness/Spec map in order to keep the cost reasonable on console."
Lots more info on the Glass Shader page. Never used it myself but I would imagine everything you'd need to know would be there.