As has already been mentioned, there are several forms of bluing, including the do-it-yourself kind in a bottle, which actually works pretty well, considering. One kind is sometimes referred to as straw bluing, I think it is, for small parts. I have no idea how it's done but the result is a sort of golden (straw) color, which is guess is why it's called by that name. I believe I've only noticed it on things like safeties on some pistols.
Some versions of CZ pistols come painted but I doubt you could achieve the same result yourself. Of course, cars have been painted for a long time and the finish holds up pretty well and much better than car finishes used to.
Browning, as was done in the 18th century on military arms, was not a natural process. That is, the metal wasn't just allowed to sit there and rust. It was a process that was undertaken by a unit armorer (for which the soldier was charged). It was in a sense a controlled natural process but apparently it was something that had to be repeated every year or two, judging from what I've read in old (very old) manuals and standing orders.
The beautiful finish on some firearms, like older Colt revolvers, for instance, is partly the nice bluing and partly the perfect polish of the metal before the bluing is applied. The better the finish, the better the scratches show.
Shoot low, sheriff. They're riding Shetlands!
Underneath the starry flag, civilize 'em with a Krag,
and return us to our own beloved homes!
Buy War Bonds.