Re: Question about uniform changes
This question comes up a lot. It seems like the TNG style was appropriate for Earth, but officers stationed on starships or starbases could wear whatever the commanding officer thought was appropriate for the setting. It's not unlike professional sports teams wearing alternate uniforms on special days (Sunday day games, for instance).
"He clapped his captain—his friend—on the shoulder. Yes, this man was very much like James Kirk, in all the ways that mattered." --Christopher L. Bennett-- Star Trek: Mere Anarachy, The Darkness Drops Again