As for colored leather, you shouldn't waste your time dyeing, ecept for the veg-tan, of course. There are plenty of sources for leather of all colors, although generally you'll have black and 2 or 3 shades of brown.
Correct me if I'm wrong, but what you're referring to would be an oil-tanned leather (or other process) that is already 'finished'. Those are unsuitable for tooling, right? I've never heard of anyone tooling on pre-dyed leather. It's always done on plain hides because they have to be cased with water, tooled, and allowed to dry, and then dyed and finished.

Do you do tooling on pre-dyed leather? If so, what kind of leather and what tanning process is it? I'm curious now.