Jennings Heilig's remarks in a discussion of the same topic, on the largescaleplanes forum:
"The cockpit color - well, that depends. Lots of Mustangs left the factory right at the end of WWII and were immediately cocooned and put into storage. The ones that were pulled out and put in service in Korea most likely had their WWII factory cockpit colors. No reason to repaint an essentially brand new airplane (ever tried to paint a cockpit on a real airplane? Think about it...). The birds that were in service with ANG units in the US that were called up may or may not have had black cockpits if they'd been through depot maintenance before going. Hard to say, and nobody is ever going to be able to prove you wrong . One possible way to tell on the latter is if the tail number is painted in the characteristic NAA tall narrow style (factory stock) or in another style (depot repaint)."
Cheers
[BTW, here's the link...it's got some good photos, too.]