I went to the LGS and picked up some 327 Federal Gold Dots. When I got home I noticed that the brass was not the typical shiny color. It was slightly darker, which I think is from oxidization (metallurgy is not something I know much about). The bullets themselves look like new.

I see no other issues. No green corrosion. Just that the brass is slightly darker.

I don't care what it looks like. I just want to make sure that this isn't a sign that it is compromised.  Obviously there's no way for anyone to know for sure but how concerned should I be about this ammo?

327 is hard to find and not popular so it's conceivable that these boxes sat on the shelf for a year or more before I got them. It is the new style boxes so it's not all that old. The boxes look fine and show no signs of water damage or any damage at all.

You should be fine.  As long as it’s not green.  I’m actually surprised they are loaded in brass cases but then again Hornady was having to load their rounds in brass cases rather than nickel plated cases due to the ammo shortage.

That's a solid point I had not considered. I checked the website and it specifies a nickel case for this ammo. I sent Speer a message to see what they say.

I was on Sig's website hunting for some specific ammo and they have a notice up that stuff that is traditionally nickle plated will be plain brass because of supply chain issues.

Speer got back to me quickly. Turns out it's from a 2017 lot where they briefly used brass. Five years explains the tarnish. I'm surprised that even in this ammo crunch it stayed on the shelf this long.

You should be fine. I have some 30 year old Winchester Silvertips with brass cases that were stored in a plastic ammo box. Still fires.  Actually a little more stout than the current loading.  It has brass cases not as shiny but work 100%