Never saw a blue JD before all I have seen have been green. The only value is with the John Deere collectors. They pay $450 for a dirty old straw hat. At one point the ladies JD were from 150 to 500ish. The tractor collecting hobby has had a bit of a down turn. The big thing to find out is if a blue JD is hard to find or did they really make one.
The tractor guys ran into the fact that they ran out of buyers for a few of reason. 1) The older guys either passed on or sold out to down size. 2) They also priced themselves out of their own hobby. 3) They forgot about the newbie the guy who needed to start with something affordable to get started in the hobby.
I did a quick check JD made 100,000 green bikes and 700 blue bikes so the blue bike has some value to john deere collectors.