[gonzo]

Either way it’s a neat card.

Normally for a card like that, I’d think it could be missing a color pass. Or a color was running very low in ink at that point, so it printed very lightly. But in those cases, the back toning would probably have a different cause than the color difference in the front.

Maybe there was some sort of impression cylinder transfer in which pink ink was on a cylinder before the card ran through. The scan of the back, with the pattern of small “bubbles” of lighter area within a darker toned base, also made me wonder if the cause might be environmental/chemical, which could affect front and back, but I’m in no way sure about that. It doesn’t really look to me like glue residue, which could be another way that a color on the front could be affected.

But given that both front and back have color quirks, it seems most likely that the paper itself has a toning. Maybe it was pinkish to begin with. If the paper in the “white“ areas of the border has the same toning, as Tyler notes above, then it could be that the paper itself was that color through and through before anything was printed on it. I wonder if you can tell whether the printing on the back is above or below the toning.

When you have it in hand, a high-resolution scan (or a peek through a loupe) should show whether the pinkness on the front is on there in the same overall pattern as the toning on the back, and whether you can tell if the pinkness is above or below the other colors.

A very cool pickup - I look forward to seeing more details!