The discoloration is just tarnish plus maybe a little color change due to heat. Try cleaning it with Brasso or some other metal polish.

I think the Dinty More stew was a 24oz can, but I'm not sure. It's 3.75 inches tall, so you can do what I do, walk around the grocery store with a ruler measuring cans. For extra fun, don't bathe that day and mumble about aliens in your sock drawer.

-Blast