As mentioned in the comments last post, I am not sure if early Breyer Bays were subject to color shifting like the Palominos. It’s possible, but I haven’t seen enough early New-in-Box Gloss Bays to compare against more "weathered" Bays, nor have I seen any early Bays where the color was noticeably different from one side to the next that could be indicative of prolonged exposure to the sun, heat or other environmental factors.
It’s definitely an issue with Hartland Bays - like many Hartland Palominos, the red base in the paint fades, leaving the models a distinct shade of green (Olive for the Bay; Chartreuse for the Palominos).
The red shift/red fade does happen with some early Breyers, but tends to be limited to those models that came with pinking of the eyes, ears, muzzle and hooves. Since it is limited to accent areas - and the absence of the pinking tends to be so complete - the lack of pinking is sometimes labeled as a variation or production error.
It’s also not that much of a dealbreaker; while we’d prefer the pinking to remain intact, most hobbyists are not going to turn noses up on an otherwise flawless model without it.
There is some color-shifting going on with Shrinkies, to be sure. Chestnuts turn peachy-pink, and Bays turn to Buckskin. But that’s a slightly different process there - a chemical reaction that is primarily a result of a breakdown of the plastic itself, and not a consequence of environmental issues. (Though excessive sunlight, heat and humidity certainly don’t help!)
Whatever other color shifting may be occurring with some Breyer paint jobs, nevertheless I haven’t seen anything green that didn’t start out green in the first place, either by design (Little Bits Unicorns, some of the Classics Blossoms) or by default (Dappled Green Bay Sham).
There’s been some recent speculation that the reason why Reeves hasn’t released any new "Christmas" Decorators may be due to the issues with color shifting or fading, especially with the color Red. Indeed, it could be the reason why the mythical Christmas Decorators might not have made it past the testing phase back in the 1960s.
But here we are speaking of a hypothetical of a hypothetical: we don’t have any confirmed examples of Christmas Decorators in the first place.
Oh, and re: other posts on the topic of fugitive paint, the most recent - I think - was the one last year about the 2013 Volunteer Clydesdale Mare. I really need to index these posts better…