Titan Fleet Yards

Man in blue suit

A man in something that looks a lot like the typical Starfleet worksuit appears in both the hallway and reception scene as well. During the reception, he is seen wearing some kind of necklace or medal, which is of course not something you would see on a Starfleet crewman. So this is probably a delegate from an unspecified Federation world, possibly Earth itself or one of its major colonies like Mars, Alpha Centauri or Vega.

Woman in dark dress

A female delegate in a dark dress is also seen in both scenes.

Man in red uniform

A man in a red uniform appears in both the hallway and the reception scenes. The uniform appears to be different from the regular Starfleet uniform. It seems like it is a red dress uniform with the gold braiding removed. There are no rank devices on the sleeves, although there does seem to be some emblem on his breast; possibly a remaining medal from the dress uniform.

I suppose this could represent some kind of Starfleet uniform, perhaps a special Admiral’s variant. On the other hand, the re-used uniform could have been just that: an efficient way to dress up another Federation ambassador, perhaps representing a major colony or a maybe human-like member race.

“Big wig” alien.

Two aliens with very large wigs are seen several times in the hallways, and also in the background of the reception scenes.

"Big wig" delegates

The same "big wigs" in The Undiscovered Country (behind the 'netted' aliens)?

Aliens with somewhat different wigs can be seen in The Undiscovered Country. Maybe these are the same as the ones seen in TOS, but as far as I know there is no behind the scenes information that confirms or denies this possibility.