Colt AR Carbine / M4 "green label"

[marktx]

Local shop has a "green label" Colt AR Carbine / M4, they tell me that the green label is significant but can't really tell me why. Did some quick searching and it is apparently the label that Colt used for a while in the '80s but beyond that I can't tell any reason why it would be particularly desirable. I'm vaguely aware that Colt screwed around with pin hole size for some rifles that makes them not particularly compatible with other uppers on the market and I would just as rather avoid if it's just another AR.