Color suggestions

Tamiya Field Blue might be a good starting point. But aside from air shows, the only blue uniform item that I can imagine on the flight line is the overseas cap that is worn with flight suits.

Normal cloth, like that used in dress uniforms, has very low saturation colors.  Using almost any blue from a jar will be too highly saturated.  After I get the color right for cloth, I usually add about 50% of same brightness in flat gray.

I can honestly say that I never saw a dress uniform on the flight line either,  but the ground crew kit I got had a dress uniform in it.  

Figured I'd use it. 

Plus I have an idea as a gag gift for my son.  He's going into the AF at the end of the year and loves Halo. Figured I'd get a master chief figure and paint it up as a Cmsgt and give it to him as a graduation gift. 

I would agree with the gray tint blue, at least from my era (early 70's).  Dress blues would have been somewhat out of place on the flightline, except for SLEB"s (self loading excess baggage) waiting to climb on a trash hauler.  Undress blues (light blue short seeve shirt, the dress blue slacks) or khakis would be seen more often, both with the fore and aft cap.

From memory  an insignia blue might be close or might have to tint around some.

Welcome first off !

For one thing it depends on the era and the changes within an era. But I think you will have to mix your own. Many airforce dress blues were/are actually a gray/blue. It's probably easier to go with a gray/blue, then add blue or gray accordingly depending on desire. Vallejo has a gray/blue but I think it's Model Color vs Model Air. Tamiya has a blue that might be able to be toned down or use it to tone up a gray, it's X4.

If you got to a good Model Master acryl color chart you might find something there.

Maybe someone else better versed in uniform colors will reply while you ponder this much.