The odd thing is mine was stored on her side yes and the side that she was on was her blue side. That side staying the same. It was the side that was up that turned green. I remember this because, when I reached for her I was like, "who is that green pony?" I saw the green side of her first and didn't understand what I was looking at. Then to see she had an even split in color was just a shock.
Crystal-sushi that is interesting that you faced this also. I am beginning to wonder if this will eventually happen to all of them unless we can figure out what caused it. Mine was free from sun and in an airconditioned room but stored in an open bag. Both sides of the pony where subjected to the plastic bag so, it doesn't make sense that one side would turn color and the other not if it was the baggy. The idea that plastic is made differently on one side seems to be a logical reason this would result.