Which Army MOS is allowed to where the foliage green t-shirts?

I always thought personnel who work with fuel or other POLs were the only ones authorized. But I see it being worn often by random MOSs.

This is from the latest DA PAM 670-1. Hope this answers your question.

Section I
Army Aircrew Combat Uniform
6–2. Composition
The A2CU consists of:
a. Coat, A2CU (see para 6–8).
b. Trousers, A2CU (see para 6–9).
c. Undershirt, foliage green or tan (100% cotton or flame-resistant material) (see para 20–28e).
d. Undergarments (see para 20–28).
e. Belt, rigger (must meet flash/flame criteria for aircrew members performing aircrew duties) (see para 20–2a).
f. Socks, tan, green, or black, tan; cushion sole (see para 20–24a).
g. Boots, combat, tan leather (see para 20–3a).
h. Headgear (see para 4–10).

The only uniform I am aware of that you can wear that t-shirt with is the Flight Suit. But perhaps the crewmember suits the tankers wear as well. It is a part of a set of flame retardant wear so it would be more about what duties you're performing I think. For example, just because you're an aviator doesn't mean you're authorized to wear a flight suit if you're not going to perform flight duties. Maybe someone else knows of other uniforms besides the flight suit that this shirt is authorized with?