Although there were obviously variations to paint schemes applied to aircraft in the field, all aircraft delivered directly from the factory conformed to a very specific set of Technical Orders governing the painting and marking of aircraft. These were also supposed to be complied with in the field too, but local commanders had a lot of leeway in approving schemes more in keeping with local conditions.
All I can give you are the finish specifications for the Stinson L-5, or OY-1 as the Marines called it, but I imagine it wasn't a whole lot different. That said, I could be completely wrong. Your best bet would to find photographic evidence and get ahold of the applicable Technical Orders in use at that time. Most WWII technical orders can be found at the NASM, NARA or the GPO. The commercial publisher ESSCO might even stock copies of the NAVAIR technical orders.
Also, as with the L-5, which had a similar role (casevac), the NASM may have technical drawings (blueprints) and the Erection and Maintence Handbook for HE-1 / AE-1 in their collection. For the L-5 / OY series of aircraft, the E&M Handbook contains a wealth of information on every finish used on the interior and exterior of the aircraft.
I'm sure you've scoured the web, but if you've missed these they are a good starting point:
If you can beg, borrow or steal a copy, check out: The Official Monogram US Navy and Marine Corps Aircraft Color Guide, Vol 2: 1940-1949 by John M. Elliott. It may not directly help with the AE-1 but it is a valuable resource.
Lastly, contact aviation photographer Bill Larkins. He has been professionally photographing airplanes since the 1940's and probably has the largest personal collection of military aircraft photos in the United States. You can scarcely pick up an airplane book published over the past 65 years that doesn't have at least one of his photos in it. Email me and I'll give you his email address. I don't want to make it public.