Up until the late 30's, most tractors were painted in grays and dull reds, which if you think about it, doesn't have high visibility, especially at night.
Caterpillar and most of it's competitors switched to "highway yellow" of one shade or other about this time. Partly in the interest of safety, and partly to make sure they were noticed in the public eye.
Euclid (Terex's predecessor) had machinery painted in a dark green shade, and later yellow during the 50's. When GM bought into the Euclid company,
they were looking to form their own identity. They came up with the Terex name, combining the latin words Terra, which means Earth, and Rex, which means King. King of the Earth, you see?
They had also done research into colors with high visibility, and that lime green was one of the best, along with bright yellows. Must have been something to it, because they paint some fire trucks this color too.
Although, that green sure looks terrible after years of weathering when it turns a chalky whitish green!
It's sort of indicative of the changing fortunes of General Motors, because at one time they had a construction equipment division (Terex, sold off) a locomotive division (EMD, sold off) an engine division (Detroit Diesel, now it's own company).
Eric Orlemann has a good book out on Euclid and Terex, which describes all this and what happened with the various elements of the Eerex corporation.
And Euclid is still in business, making off road trucks.
Hope this helps,
alan627b