I have a think book "John Deere - History of the Tractor" by Leffingwell. It's a Deere publication.
It shows pre 1910 John Deere carts and implements in green, before they had tractors.
In 1911 they looked at buying and reselling Twin Cities tractors, which were grey and red according the photos in the book.
In 1915 they came out with their own tractor, which was green with yellow wheels.
In the war years they came out with industrials in yellow as well.