As far as I can tell, this is a more common variant of Chewbacca that made appearances on all ANH cards (12 back, 21 back...). If you look, all of his limbs are slightly green in color and the body is the intended color his limbs should be. Since the bag is attached to his leg, it too has more of a green discolored hue. There is no real reason behind the variation, they just made them this way and released them despite the color error. If I find out more about the reason behind this color variation, I'll let you know. It's kind of the same as the yellowing stormtrooper phenomenon. It just is the way it is...