Here's the way I understand WW2 US Army uniform regulations concerning the wearing of rank and branch insignia on shirts and overseas caps for officers of the Army Air Force. Others should correct me if I'm wrong.
Prior to August of 1942: Shirts were worn without collar insignia when the coat was worn. If the shirt was worn as an outer garment, rank was worn on the shoulders, US on the right collar and AAF prop-and-wing on the left and on the matching (OD or khaki) overseas cap. Aviation cadets wore a visor cap with a blue cap band and the large 3" cadet insignia while a 1" version of the aviation cadet insignia was worn on the overseas cap.
After August of 1942: Shirts were worn without collar insignia when the coat was worn. If the shirt was worn as an outer garment, rank was worn on the right collar and AAF prop-and-wing on the left and rank was worn on the matching (OD or khaki) overseas cap. Aviation cadets wore a 1" version of the aviation cadet insignia on the overseas cap.
I think it would be a very rare occurrence for an officer of the United States Army Air Force to show up to an awards ceremony in Class As and be out of uniform (in other words, in violation of uniform regulations).
MattS's post about overseas caps (renamed “garrison caps” in 1940) brings up some interesting questions…
These caps came in 2 flavors:
Olive Drab #51 “chocolate” in wool (winter), and Khaki #1 in cotton (summer)
You mentioned that either could be worn, however, judging from most (not all) of the photos in this post, it seems that USAAF servicemen wearing a khaki shirt are wearing a khaki cotton garrison cap, and servicemen wearing an OD #51 chocolate wool shirt are wearing an OD #51 wool garrison cap.
Let’s say it’s 1943, and I’m a USAAF field officer (2nd or 1st Lieut., Capt., Maj., 2nd Lieut., or Col.), stationed in England. I’m going to a big dance, which I know will be a great morale booster for my men…
In the movie, “Memphis Belle,” there is a dance scene with a big band in a hanger, where all the servicemen are wearing their Class A winter tunics. Some also have their Class A service caps (but are not wearing them). Even though they are in England, where the winter uniform was usually worn year-round, there is no way that you could dance in one of those heavy wool uniforms, especially with the addition of a wool shirt and heavy wool “Pinks” trousers. I played in a big band for years, and have also danced to them, and I swear I didn’t know my body could produce so much sweat!
Perhaps they just got it wrong in the movie, but in most of the WWII photos I see of servicemen dancing to big bands, it appears that they are wearing Class B lightweight khaki shirts and trousers, and they arrive wearing the khaki garrison cap.
Perhaps rank has something to do with it; I could see how enlisted men would arrive in khaki Class B uniforms, and be going nuts picking up all the “birds,” working up a sweat, doing the Lindy Hop, etc. And maybe the officers, being older men, might already be married, and might not be into swing music, coming from an older generation; therefore, they might arrive in their Class A tunic and service cap (to keep up appearances and respect for the rank), and just watch. Or were ALL servicemen supposed to wear their Class A uniform to social events?)
The reason I bring this up, is that I go to a reenactment each year where I live, and I’m going as a USAAF colonel because of my age. (I could never pull off being a cadet!) I would be wearing the Class A wool tunic, wool pinks shirt, and wool pinks trousers. If I wanted to dance with my wife, I would need to remove my tunic, place the appropriate pins on my shirt collar, and dance away. (I don’t think there was a “Pinks” garrison cap, so if I went to a dance without the tunic, I guess the OD garrison cap wouldn’t clash as much with the Pinks shirt as the khaki garrison cap, right?
(Sorry this was so long.)