For the NVA I think there is only one type, and it has a dark collar. However, there are different levels of quality. Not sure if the differences are age or rank, probably both. I've got one that is made of a very rough, extremely poor quality wool like material and others that are made from a very smooth highly synthetic material (dunno if there is wool in there at all).
The ones with green collars were for the Grenztruppen (border guard), so that might have been what you got originally.