Early Magazine Question

I have a question regarding an early (pinned, two-tone) unmarked magazine pictured below:

https://www.milsurps.com/images/impo...01b3c365-1.jpg

The upper, normally bare steel portion of this type of mag has in this case a red-brown coating that would suggest unintentional rusting. However, this layer is so even and fine, I have second thoughts. There is absolutely no scabbing, blotching or pitting. Other than the color, it looks like an intentionally applied surface, like an ultra-fine parkerization (again, color aside). Is this indeed just post-manufacture rust that I can remove without remorse? TIA!

Looks more like someone with no knowledge of why the top is bright tried to correct it by bluing or coloring it some way.

It looks like browning used on muzzleloaders.

Thanks, I'll forge ahead with removing the rust. Now, vinegar, molasses or naval jelly?

The two-tone mag's were issued during WWI. They do bring a premium and I have seen a few for sale for around 150 to 200 dollars. There are a few that have a lanyard ring attached to the bottom and they bring a higher price.

Originally the Colt magazines were tempered, and then heat blued. The heat from the bluing process was removing the temper from the top of the magazine, so Colt started bluing the magazines, and then tempering the magazines by dipping the upper part in molten cyanide at around 1600f degrees and then quenching in oil. This process removed the blue where the magazine was dipped. When the bluing/tempering process was changed, all of Colts pistol magazines from .22 to .45 were done this way up until 1940.