Purple Stained Cases

I recently received the attached photos showing a .223 case and a .40 S&W case. These were found in the desert at a place where people go to shoot in southern New Mexico.

The cases are nickeled brass with a purple stain on them. One close-up of the .223 case appears to show a cannelure just below the case mouth (possibly indicating a blank or reloaded blank case) though the cannelure is not visible on the other photo.

The question that the sender has is why the purple stain? My initial reaction is that someone has simply marked the cartridges in this way to identify handloads, but I have to ask if anyone has further information or thoughts?

There is a lengthy thread here on the .40S&W. Odd purple Winchester .40S&W training ammo

The .223 is the same scenario - a government contract for some a U.S. agency that for whatever reason wanted to have cases on those two calibers which were readily identifyable vs all other ammo. The order was vague about the color, and Winchester settled on purple . These were done in 2014, 2015, and 2016. Not sure if made after that.

Weren’t these for the homeland security folks?

Yes Alex they were but several companies have been offering them for commercial sale here in the US.

Thanks Guys. I obviously missed the previous post about the purple Winchester contract. If they’d done it with .450 Short I would probably have read it !!
Chris P.