Green,
It depends on which time frame you want to build. The Buff has been around so long it has seen many changes.
The natural aluminum was the first "paint" scheme when it was a high altitude penetrator. Followed by the camo, I believe south east asia camo, when it started low level penetration. Now it is in the grey camo.
I belive that the interior parts were zinc chromate. They could have changed then though.
Hope this helps