JamesTKirk

In the Original series, the green uniform that Kirk sometimes wore was never really explained, but since he was the only one who wore it, the implication is that it was some sort of special issue uniform just for Captains, or those in command.

Actually, the green uniforms (both of Kirk's wrap-arounds as well as the dress uniforms worn by Command personnel) were the same shade as the standard ones, which were also green. But they were made out of different material, so the standard uniform showed up as yellow under the lights and on film, and some stayed green. Later the green was "canonized."