Cold bluing or cold blackening seems to be an accepted method of protecting steel parts in the shop. Add on a sealant or keep the part oiled and supposedly it will resist rust and corrosion indefinitely.
I have done cold bluing in the ancient past using the gunsmith supplies. When I was a kid I stripped and refinished and old Sears .22 rifle, and I built 4 different black powder kit guns that came in the white.
The quantity in gunsmith supplies is rather stingy. The amount in a bottle is enough to do a fair to good job on one complete firearm and maybe do some touch up work if you know how to make it blend. Two guns if you don't make any mistakes.
More recently I've started making tools in my own shop. Many were intended to be a single use or short run tool. Long reach clamp to hold a slide bar in a mold until it could be match machined and clamped in other ways. Long reach tool holder for deep milling. Half round tool for work stop in the spindle and work positioning. Lots of stuff really. Mostly I have left them in the white (fine for carbide tools and some I've made in stainless) because they were made to do a single job. I didn't throw them away, but I didn't plan for them to be likely to see future use. It turns out nearly all of them have been much more useful than I originally planned. I need to blacken and oil them I think.
Not wanting to go with a stingy little bottle from a gunsmith supply I looked at McMaster and MSC. They both stock some form of steel tool black. It seems expensive, but its a larger quantity than your local retail bottle of gun blue. How long does it really last? Is the "sealant" in some of those kits better than just oiling the part? Is it just oil? I don't mind spending the money. I just want to know its worth it.