if it runs ok on high throttle may just be an adjustment. I have talked to old some Sears repair guys and knew a couple guys that worked there at Sears selling them, and it seems that the orange and blue ones wasn't so much a "year" thing as it was the orange ones were sold at a cheaper price point than the blue ones. Another guy I have known for years has a '67 like this and it's blue, never been painted, he has paperwork from when it was bought brand new by an uncle. Blue ones were more likely to have headlights, a tail light, cig lighter than the orange ones.
I have seen earlier 60s models that were also blue.
I live only 30 miles from where I grew up, but now I am only 3 miles from the plant where most of these machines were made. I'm always hearing "friend of friend" stories of people who worked there.