Ruthless welcome. I'm a fellow Pittie/Dog lover and volunteer quite a lot of time to bull-breed rescue.
I have recently started to do custom dog collars to sell. Its a real trial and error experience I have gone through a few different options; when working with tooled leather I like to use Eco Flo Hi-lite, neatsfoot oil and a wax topcoat(I have been using Snow-Seal for its waterproofing quality).
For dyes I use Fiebings, let it dry overnight, deglazer(Nail pollish remover) and then neatsfoot oil, Carnauba creme for the front and Gum Tragacanthfir the back and edges.
As far as pre-dyed leather it limits you to only a few options and cost is always more. I am always a fan of doing things myself whenever possible. Anthing he can do I can do too, or atleast try.
Here is my Girl: