Home Forums Hunting & Shooting Ask The Gunwriters Brass color/age question

Unfortunately, one of my neighbors lost his father. The gentleman was 81, and a hunter and reloader.
My neighbor gave me a Samsonite travel/bowling ball bag stuffed to the gills with 30-06 brass.
He stored some of it in old Remington boxes, but most was loose or in plastic Federal retainers.

As I've been cleaning it up, I have noticed that some of the brass has a darker copper look to it. The
pictures don't show it well, but there is a difference. The headstamp tells me it's a little older.

I don't have any experience with brass cases older than the mid '70's, so I'm curious if these darker
cases are a product of age, copper content, ammonia? Nothing important here, just looking for education.