Probably the Panzer Gray, or possibly RLM 66 Schwartzgrau. In the way that Olive Drab was the U.S. "Army color", Panzergrau, which according to Tony Greenland is called Schwqrtzgrau in official documents, was the "Wehrmacht Heer color" early in the war. He suggests that most out of the bottle paints need to have some blue added to get the tone right.