Problem is, these areas showing bright bare metal would quickly rust over in the outdoors. Furthermore, the turret was made of cast steel, was primered underneath and probably had a darker "complexion" than typical auto body stamped steel. Think 'cast iron skillet' and you may have your answer in regard to color.
-Harq
ORIGINAL: Didge
Thanks for the comments guys.
Before I started building the kit, I sprayed the lower & upper hulls, turret and various other bits in Tamiya 'Bare Metal Silver' (AS-12). I cut up small pieces of an old bath sponge, put a little Humbrol masking fluid on the sponge, and dabbed it on the places that I wanted to show bare metal.