In the original Star Trek series, gold uniforms were command, red uniforms were engineering and security, and blue uniforms were science and medical.
In The Next Generation, Deep Space Nine, and Voyager, red uniforms are command, gold uniforms are engineering and security, and blue uniforms are science and medical.—Preceding unsigned comment added by Icecreamdif (talk • contribs)
In the Original series, the green uniform that Kirk sometimes wore was because of a change of lighting while on set filming was taking place. The normal green shirt that Kirk wore showed up as Gold on film just as beige shirts looked red. This was because for some reason the shirts colors would look different depending on how much light was shining on the shirts. (Source: https://en.wikipedia.org/wiki/Star_Trek_uniforms) 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."
Blue is the only color that meant the same in the TOS pilots, TNG on, and ENT, although the shade changed sometimes.
(random contribution: sources very difficult to find without watching all of TnG and Voyager) - for those two seasons there are green uniforms in addition to red yellow and blue - these are starfleet's military uniforms.. perhaps it would be better to call them "ground forces" .. anyway, there you go. – The preceding unsigned comment was added by 126.96.36.199 (talk).