The color was put into the casehardening process to "show" that the parts were case hardened. Visual proof of the quality right there for every one to see. and sometimes, counterfit..
Have or have had both guns, in 7.5", the Vaquero in .44 Mag was stainless. I'm a reloader, and have been into the .45 colt for 30 years. Not so much of a .44 Mag fan, although it do have some. My Vaquero .44mag went away in favor of a Super Blackhawk, because I wanted the adjustable sights.
Come to find out I'm not crazy about the feel of the Super Blackhawk, I think because of the very slightly, but noticeably different hammer and trigger. I've spent so much time shooting my Blackhawk .45 the Super feels ...funny. The Vaquero .44Mag felt the same as the Blackhawk. Hammer spur in the same place, smooth trigger, etc...The only real difference was the rounded edges o the frame and the fixed sights.
All else being equal (and it almost never is) bigger bullets tend to work better.