In my opinion and many others, judgeing by resale value, the best mid-size tractors are the "big 2": John Deere and Kubota. That said, I have heard of several complaints from Kubota owners about overheating, but none from JD, so green would probably be your best bet. To be fair, these might be isolated incedents affecting only certain models, and the odds are also very good that you would not have a problem with an orange tractor. I cant make my 43 hp JD run hot even while cutting thick bush all day long in the summer with a 6 ft cutter and a radiator screen that could use cleaning.
The only overheating I've heard of with kubota is when owners didn't know they need to clean the radiator screen. Happened to me ONCE. That isn't a problem just simple maintenance.