Rust-brown was the old style of bluing.
There are Plum-Brown Birchwood-Casey kits that give the same look.
Follow Their Directions Precisely!!!
If you go with a Cold Blue, there are a few things to know to get a good looking finish.
First...Prep Prep Prep Prep Prep...and then Prep some more. Be as OCD as Monk about Prep.
Good enough, ain't enough, not for cold blues. Its gotta be dang-near Perfect.
The more prep you do, the better the finished result.
Second, do it in a WARM room. The warmer the better. Cold is your enemy with cold blues...strangely enough.
You'll want an 80+ degree room...constantly warm...it helps the bluing to soak in better (don't ask me why, I ain't no scientist).
Third, apply liberally...its the only thing I do in a liberal style
Put plenty on.
Fourth, after a few days of letting the the bluing/browning stuff do its thing, smother it in Cosmoline,
and stick it in a storage bag for a few months in a relatively warm room.
That helps the bluing/browning cure nicely.