Laurent,
On this tank it seems to be more about when it came back to the factory for it's upgrade. As for the interior colors I think they are the original colors as Ft. Knox is a US Army post, and most of the volunteers who work there are ex-Tankers, they would have painted the interior gloss white, as a US tank, not take the time to paint only some of it all these different colors.
Here is the Patton museum's SDKFZ 223 100_3813.jpg
It's a off white color everywhere.
My 2 cents.
Dan