I would call that Panzer Grey based on color plates in the books I have and the model paints we have available today , but they could be wrong . Might I suggest you go to a site ( Missing-Lynx ) where the guys who write the books , research WW2 vehicles in museums and archives and advise the model companies hang out . Guys like Hilary L. Doyle , Steven Zaloga , David Doyle ( authors you might have heard of ) and many others . Right now there a couple of threads on German paint schemes / timelines being discussed by guys who have original WW2 German paint chip cards . These guys really know their stuff , if you post on there I'm sure you will get the answers your looking for