I'm not sure if this has been suggested or not, but...
I think that, when you visit a tailor, you should have the option to customize a "Crew Uniform". It would be similar to Captain/BOff customization, except that you can't change Head or Body; only Uniform. When finished, the changes would apply to all the members of your crew that roam your ship's interior. It would also be worn by ground actions that summon crew members, such as Security Escort, show of force on Nimbus, and DOff reinforcements.
The only limitation I can think of (albeit a limited one) is that any option not available for all crew members of your respective faction, such as Orion Bikinis and Lohlunat sunglasses, would be unavailable in order to prevent rendering errors and other derpy appearances.
Space... The final frontier... These are the voyages of the Federation Starfleet.
Its continuing mission: To explore the same old worlds...
To blow up enemy life and hostile civilizations...
To boldly push F where everyone has done so before!
...And there should be three slots (chosen from randomly when the game spawns its random officers for the interior of your ship). You should be able to buy more slots, though, up to a maximum of like 10 or 12.
These are the unoriginal voyages of the starship Aether. Its continuing mission: to explore boring new worlds, seek out Dilithium and Reputation, to boldly go where everyone has gone before.
To make things easier on the dev team, we could be allowed not to fully customise the uniforms, but to simply choose from a small number of templates. We'd get to choose colours, and to point out which uniform part should bear the class colour (red for tactical, yellow for engineering and so forth). Since making fully cusomisable crew would otherwise require a great(er) effort as well as a greater risk of bugs and glitches, I think this would be an acceptable compromise.
Also, just because it bugs me, it would be nice if they finished the character skins, so if i decided to use open uniforms, my crew wouldn't look like they all had horrific farmer tans from the neck down.