I think it's because the metal used is different than the slide itself. Could be the same finish, but it takes differently to different metal/texture. The extractor/loaded chamber indicator also patinas differently. If you notice some pics, it often turns purplish over time. Totally normal. Even brand new, these parts appear a little different.

 

The heat treatment of the metal will cause the anodizing to not adhere/stay in color. Hence the purple color. P7s had this issue as with certain batches of Bushmaster receivers.

 

It is not anodizing, the part it not aluminum like AR lowers.

 

MIM

 

Is this the patina of which you speak?

As stated earlier, the hardening process of the metal prevents the HE finish from adhering to the metal. The metal is still protected, so it is purely cosmetic.

 

This is what I meant. My german made HKs have this issue, the US made one is still black.

 

Man, that looks bad though...

 

Nah, just gives it character! I have considered sending the slide release levers out for refinishing but there is no guarantee that any other finish won't do the same.

 

Honestly, the lever in that picture looks rusty. Maybe it's just the lighting?

I know the extractors turn purplish, but I've never noticed a color change on slide stop levers. Well, I shouldn't say no change, mine have gotten shiny on the corners/edges.

 

Rust is Patina. :0)

 

It's definitely not rust. What you are seeing is the copper-colored underlying metal with a mottling of the remaining black finish. If I keep this up, one day it will be bright as a new penny.