According to the script notes for Star Trek VI, among the crowd were "the Klingon and UFP Presidents, complete with advisors, retinuies, entourages and attendants [….] The place looks like the UN Security Council + the Olympics. All color coded..."
The script continued to describe that Pod #1 was designated for "the Federation Delegation (Green)" […] Pod #2 for "the Vulcan delegation (Yellow?)", Pod #3 for "the Klingon delegation (brown?)", and Pod #4 for the "Earth (green) delegation...." The final color coding, however, appeared to more accurately depict the following: green for Earth, red for Klingons, yellow for Vulcans (and perhaps Romulans), and blue for the Federation.
One of their costumes was sold on It's A Wrap! sale and auction, which described the costume as "a mask and wig worn by one of the Khitomer attendees, the mask is dark-gray, molded plastic featuring various textured accents meant to emulate some kind of hardware or circuitry and a mustard-colored open mesh over it. Also included is a curly-haired wig in various shades of brown that falls long in the back and a purple conference sash." 
This flag bearer was visible outside, carrying a flag, while leading the Federation delegation into the building where the Khitomer Conference was held in 2293. He stood about the rear of the room along the wall while the conference took place.
According to the relevant call sheet, there five male and five female flag bearers present at the conference.
The president's assistant was played by regular TNG extra Lena Banks. The other three dignitaries were played by Roma Lee Tracy and two unknown actresses. Neither of them received on-screen credit for their appearance.
The name of the race, described as "'Silvertube,' an Amazette alien", was directly from the actress.  She was shooting the scenes at the Brandeis-Bardin Institute and was chosen to portray the Federation President's assistant. It was decided that she should play his "eyes", because in an early version the president was blind and she was therefore to guide him. However, the scene with her and the President was ultimately cut from the aired film. In the finished film, she is only visible in the background, but the cut scene was part of the film's theatrical trailer.