The majority of play during Nighthawks takes place in the downtime between missions, on the Charys. Aviators are off-duty, or helping to plan the next mission. As such, you can pretty much wear anything and costuming is entirely optional.
Some suggestions if you do want to costume:
Taking inspiration from either original or modern Battlestar Galactica costuming is fine.
Overalls worn with belts can suggest a flight suit. Since the aviators are from a mix of backgrounds, there will be no standard colour.
Your colony of origin can be suggested with jewellery, temporary tattoos, insignia if you like. Both astrological logos, and more interpretive symbols suggesting twins, a crab or bull are fine. Avoid symbols of the other nine colonies unless you have a background reason.
Military details for characters with that background are fine too – but you’re off duty, and won’t have access to guns when on the Charys deck.
Inspirations for Patches, etc
Anything that suggests your colony, or military/civilian background… Zodiac signs for colonies are fine. You can borrow BSG or Marine aviator style for military, wings, ship names, unit names, etc. For civilians, you can wear absolutely anything – just not military. Don’t confoorm
Jewellery, Pins, etc
Civilian Aviator Pin