I have a couple pedersolis with that finish. It is their version of barrel brown. It’s more like a paint and will scratch off. I was gonna rebrown mine so I’ve tried to remove it with vinegar and blue remover but neither worked. I’ll take more drastic measures eventually.
possibly they didnt use baking soda to stop the rust process. when i rust brown i always wash good with baking soda water when i get to the color i want. it stops the rust. they may be too lazy to do this.
It was meant to represent/replicate the old plumb brown, chemical process to the metal. Pedersoli stopped doing this years ago, they now use a bake on Dura coat. I think the old stuff is better than the new paint on stuff, the finish you have can just be wiped with light oil and will continue to age, the new stuff chips and scrapes easy.
Kinda like this,
The guys shows it finished in this video, you can see the plumb tone.
It’s factory made so they want something fast and cost effective. I recall an old Navy Arms Harpers Ferry 1803 in the .58 minnie ball barrel that had that color. I did a CVA kit with Plumb Brown and it looked like that. I got it off with navy jelly and steel wool and redid it it came out more brown. I thought it was a failure on my part to degrease well.
I think it happens when the blueing temperature is slightly wrong. Has happened in the past as well as now. I have a pair of second gen Colt Army 1860's that have the plum brown colour. I actually really like it , it is a good colour and makes them a bit ,more unique.