Note your heading included ‘Green’ tractor. Mostly this implies age of the tractor and some cosmetic difference. I do not know when the YM2000 when from green to red, while there may have been minor mechanical changes, any major changes typically changed model numbers in some manner. An example would be the power-shift transmission changed the last 2 digits to xx10 and later to xx20.
The green to red did change things like the headlights from the side of the front to above the grill.
There were probably other changes, but typically not major mechanical stuff.