Hi George
Welcome to Armorama!!
Dana Bell wrote an article about U.S. WW2 interior colours for FSM October 1997. It makes for interesting reading, because the Army and Navy seem to have disagreed about the colour to be used, and there were many exceptions to the regulations... so there's scope for most colours to right to some degree...
Bronze Green, Dull Dark Green, Interior Green and Medium Green were all used at some stage. Not mentioned in the article, but noted in Detail & Scale's P-39 book is "Bell Green" - their own "company colour".
As for Olive Drab, Dana Bell says it was specified as the interior colour for the Piper L-4 Grasshopper (and AT-6Fs from Sept 1945).
Hope this helps, rather than confuses!!
All the best
Rowan