Don, this is another very good question and to answer this question have a look at the picture below in particular the light patches above the drivers port and the left side of the front notice the light area

And confirmed on this colour picture

This has puzzled me for some time as all German tanks where painted with red oxide primer which will show as a dark area on a BW picture but this area where the zimmerit is missing is light Why, the reason is when zimmerit is knocked off sometimes a residue is left behind covering the red oxide primer as confirmed in this picture of a Jagdpanther with a small patch of zimmerit removed notice the red just showing through the zimmerit

And here on this recovered turret