When you look at their top, they just look bizarre and unclean: the yellow one is not of the bright lemon usual color, and the green is unpure, and darker as the vintage green.
But if you turn them on their belly, you can see light smear of other pigment frozen in the plastic.
It is now clear those should be rejects. While watching at Maikel Mei's one, so perfect, it could have been a psychoedelic series, made on purpose. But mines are obviously the result of changing the color of the batch in production.