Not sure if it is the same but on a couple of my shotguns I have a matte nickle coating that some call french grey. It provided good corrosion prevention but is not that durable and once worn then corrosion is an issue. I have to polish with Flitz at least once or twice a season. I have also seen matte finished chrome for a similar look and if hard industrial chrome the corrosion protection is one of the best.

These are sort of faux French finishes. The original was just an acid etched bare steel. Later it was either bluing or case hardining with the color removed by acid treatment. This would give some protection but not much, much less than the nickle or chrome. If I had anything color case hardened I would want the color. Treating with casenet also produces a french grey effect as it is case hardening with out the colors. It improves wear resistance but not much better than bare steel as far as corrosion resistance.

On that rifle I think cold rust blue is the way to go as everything else is classic.

"When you disarm the people, you commence to offend them and show that you distrust them either through cowardice or lack of confidence, and both of these opinions generate hatred." Niccolo Machiavelli