you could do a normandy scheme, for my panther i used olive green, dark yellow, and red-brown camo paints from tamiya and humbrol. as for the tanks i have no real clue about them except early panzer IIIs had a 37 mm gun until it was upgraded with a 50mm gun. And as for panzer IV, the ausf e had a low velocity 75mm gun for infantry support, i could be wrong though so dont take it as gospel.