As you may have noticed from one of my posts, I too am building a stuart from academy, but mine is the M3A1. I have tried to do some research, and I have come to the conclusion that the inside of the drivers, and the assistant drivers hatches would be white. However, I am pretty sure that the turret hatch would have been painted the same color as the exterior. As far as the interior, it would be painted white. The fire extinguisher I would assume would be red, and the shells would be brass, the radio (I think) would be OD, the seats are black, and I think I remember reading that the main gun was painted OD on the inside.
This site might help, but you will find that the “honey” kit from academy has some faults with the interior.
http://afvinteriors.hobbyvista.com/m3stu/m3stu1.html
Good luck with the build. You might also try a google search. I did this for my research, and found a plethora of “honey” pics. I’m sorry but I did not bookmark most of the sites. It did take me a while to find them, but they are out there if you look hard enough.
http://www.jed.simonides.org/tanks/mike-number-us/m003_light_series/m3light-series.html
edog