Processor? Or maybe storage.
I always assumed the color shirt on my Ektachromes had something to do with the processor, since some of my rolls were processed by Kodak others by Drewry. But when I went back and looked more closely, sorting through the numbering and subject matter to reassemble shots by roll, it turned out that some frames from a roll had shifted and other frames from the same roll were as good as the day they were shot. So all I can suggest is maybe storage or useage...perhaps projecting an Ektachrome accelerated the shift...although even that does not readily corrolate with my stuff. I remains a curiousity for me. Here is an Ektachrome that looks as good as it did in 1960:
1960 Ektachrome
JBWX