According to Peter at Turnbull Restoration, both Uberti's and Pietta's case coloring is fake. It's not hardening at all, so I don't call it that. Pietta's process is pretty much identical to what Ruger used to do on their Vaqueros.
Uberti seems to use a slightly harder steel than Pietta, but Uberti's quality control has dropped a bit. I just ordered a Euroarms Remington and am eager to compare it to the others.
As for stripping the orange-red paint off Uberti's grips, the best process that I've found is to use a couple of applications of Citristrip gel. It won't harm the wood, and it takes the orange off nicely. After that, I add a few coats of Watco Danish Oil - Medium Walnut, and the grips are totally transformed.