This is not "recent" retoning; it's existing toning that's not showing up in the seller's photos. The angle of the slab in the seller's photos—i.e, tilted slightly away from the lens (particularly in the first photo—about 15º; less in the second)—is going to provide the most flattering view of any slabbed coin. It's going to hide surface defects and can also conceal tonal changes. You can try this by holding any slabbed coin at this angle away from the lens. The "average, ambient" room light under which the photos were taken will also soften the look of the coin. The OP's photos, by contrast, were taken under a harsher, more direct light and are showing a truer surface. I'm not suggesting the seller was trying to dupe the buyer; angling the slab like this is just an easy way to make the coin look its best and you see it on ebay all the time.
It's not just the seller's photos that look clean, NGC's do too. Enter the cert number in their verification page and you will see.
Really doesn't matter. It's quite easy for toning like that to not show up in pictures or for the coin to look completely different in 2 different pictures. Look at this coin for example. I took both sets of pics myself, and all I did was change the angle of the camera and lights very slightly. See what I mean ?
I understand; you made this clear in your first post. Look at the reflection of the room in the surface of the slab in the seller's photos—the top half is lighter than the bottom. Even that subtle difference affects the look of toning in the coin: the lighter surface being reflected clearly is showing less "existing tone" than the darker surface. And look at Doug's photos.
To be fair, this is not the same scenario. You can still see the darker toned areas on your coin in both sets of pictures. The only difference is that they look black on the first set and metallic blue on the second set. On the OP coin, in seller pics you see some small dark areas that are also visible on the OP photos, so it's not a case of lighting or whatever making dark areas invisible. Actually the few dark spots that match up on both the seller and the OP pics, they are more readily visible on the seller pics. Either the seller just used old pictures, or the coin spent some time in a relatively high temperature situation along the delivery route. Since your seller is in NJ, you are looking at sauna temps in a mail truck sitting in the sun. We have been having a weeks long heat wave around here.
Actually the package was delayed. It left New Jersey last Tuesday night and didn't arrive in Alabama until the following Monday. Could this have caused so much toning in such a short time? Maybe this explains the mystery.
The point of Doug's photos is to show that dark areas can appear lighter or even disappear—and light areas can appear darker—under subtly different lighting conditions (and angle of photograph). It depends on what precisely is happening on the surface of the coin. In the case of simple tarnish, the fact that the seller's photos do show some of the dark areas—but not as intensely—shows this to be a lighting/photography situation. As for heat damage, sorry but this sounds absurd. Coins have been shipped around the world during the summer months for years; they sit in hot cars, hot safes in garages, hot boxes in attics, etc. Do you often read about pronounced toning changes from these situations?
Could have been some residue on the surface that reacted to high heat. It's plausible rather than absurd.
Almost anything is possible. But in the end what really matters is what is the most probable explanation ? And in this case the most probable is that it is the pictures and nothing more.
May very well be the case. The odd thing is that some of the dark areas do show, while others don't. This one's a bit of a brainteaser and Rorschach for sure.