I got an amazing rainbow toned ASE from a dealer who bought it from someone who stored them in his auto shop to keep them away from his wife, so you could try that.
I had a tube of Franklin proofs that was only 3/4 full. The rest was filled up with acidic newspaper from probably the 1970s. Over the years, this would-be CAM reverse became a disgusting black. Technically I guess that's "natural", right? I've currently got that same paper up against a 1922 Peace, in the hopes that I can remove the paper before it gets too far and end up with something nicer. I'll be back in 5 years for results