It looks like natural toning to me. I guess if you like this kind of toning then look for proof eagles in PCI holders. If you don't like the toning then look for something else. I also wonder if say putting them in a Whitman album would make them tone in a similar way over 15 years or so. I have other silver coins that were put in Whitman albums many years ago and they are toned now. But they are not proof and none look anyway near this much toning.