Another new member, my first post.
Thanks to you present members! I have learned a lot from you before buying my YM240. Now I hope my research can help another new buyer. Here's what I found regarding the lime-green tractors imported by YanmarUSA in the 1970's and 1980's. I don't know how much of this applies to the tractors first sold in Japan.
Below is a reference to a 1979 sales brochure illustrating the second-series YM240 that I bought. It's green and the headlights are in the grille. According to the serial number mine is at level 'Design Change Mark #3' so I estimate it was manufactured about 1979 or 1980.
After the manufacturer's tractor brochure is a dealer's implement brochure. The dealer showed a first-series YM240 with his implements. That model's hood opens like an automobile. My YM240 parts manual (for "tractors manufactured after 1975") shows 'Design Change Mark #2' for first-series hood hinges, so apparently the second series with forward-tilting hood began at Design Change Mark #3.
The parts manual shows Design Change Mark #4 as the final revision to the YM240. Perhaps someone else can post to clarify if these last YM240's were painted red, and also if the change from green to red ocurred earlier in Japan than on the American-market tractors.