When did the Germans make the switch from Dunkelgrau to Dunkelgelb for their...

Lert: I'm about to get model of a StuG III Ausf. G, a variant that was produced from 1943 to 1945. When was the switch from gray to tan as base color for armored fighting vehicles? This will help me determine how to paint my model.   Is it conceivable that Ausf. G StuGs drove around in dunkelgrau? Or was it all dunkelgelb by the time the G variant came around?