This is scratch gate circa iPod nano all over again, where apple had no idea it was going to do this and now suddenly has to scramble to come up with some PR answer for whoops we screwed up and the way we got it that color was subject to pre-mature oxidation that we did not expect. They can not just change the process now, so what do you do, well you lean on they must be doing it wrong, when in reality it is probably a manufacturer variation in the coating / coating supply that is allowing for these to be more subject to rapid and unwanted oxidation.
They need to go yep we found the culprit, it is X or Y return them and we have tighten our already tight tolerances even tight to make this not a thing going forward.
I just wished apple had the stones to be like yep we did that, we had no way to know cause we tested it.