I have been up close on this aircraft myself and from what I could tell it was not painted at all, it looked to just be steel, I remember a documantary saying thy had to create heat resistant paint for the red stars because the paint kept peeling off but didn't menation the rest of the aircraft, plus when I was next to it, it just looked like unpained steel.
Have a look at the photos I have.
The landing gear was obviously painted a light grey but in the photo below when the sun hits the aircraft you can see that the matt grey is actually unpainted metal. I think maybe some of them may have been painted however this one wasn't.
Anyway I hope these photos help, I wasn't able to get to the back of the aircraft as it was off limits however I'm sure you have see the back of it before.