The last pic shows the color on the oil pan vs. the engine in the background.
At this point, I pretty much know the color (blue/gray) and just cannot find that engine paint. I might just match the oil pan to the gray of the rest of the engine, painted back in 2009.
Your picture (attached,) appears to show blue paint on the INSIDE of the oil pan. That definitely would not be original, as GM didn't paint the inside of oil pans. [on edit] Sorry, it's an optical illusion thing on second look.[/edit]
I think you'd be happy with any of the blue-gray paint that the usual suppliers (The Filling Station, Jim Carter, etc.) have. What I got from Jim Carter matched the remnants of paint on my engine exactly, which isn't really necessary. Even if you park your truck next to someone else's, and the "original" engine colors are slightly different, you wouldn't be able to tell the difference. See what Phil said above about factories mixing their own engine paint.
Don't overthink it.