Color or hue was a characteristic of visible objects dependent upon reflection or absorption of light and an individual's ability to perceive it. All colors fall somewhere on the color spectrum. An impaired ability to see color was known as color blindness.
Factions, countries, and interstellar powers which competed against each other were represented by colors on their clothing and flags. (TOS: "The Menagerie, Part I", TNG: "The Last Outpost", VOY: "Nemesis")
For many generations on Triskelion, the collars of obedience identified which of the three Providers owned a thrall. Each Provider was represented by a color – red, green, and yellow. The master thrall had a collar with all three colors. (TOS: "The Gamesters of Triskelion")
In 2152, obsessed with developing a new command chair for Captain Jonathan Archer due to mind-altering radiation from a trinary star system, Malcolm Reed asked to run some color-choices by Commander Charles "Trip" Tucker for the headrest. Archer commented that he cared not what color the headrest was or whether it could serve him iced tea, that he just wanted a place to sit. (ENT: "Singularity")
In 2254, when he was a captive of the Talosians, Christopher Pike was informed that if he found the form and color of the protein complex in a vial unappetizing, it could appear as any food he visualized. (TOS: "The Cage", "The Menagerie, Part II")
In 2263 in the alternate reality, Doctor Leonard McCoy attempted to distract Spock by asking him what his favorite color was, just before cauterizing his wound. Afterwards, he explained that it was said that medical treatment hurt less when surprised by the pain, a theory that Spock described, using colorful language, as "horseshit." (Star Trek Beyond)
Starfleet vessels, by the 23rd century, utilized a number of colored alert signals, such as yellow alert and red alert. (Star Trek III: The Search for Spock, et al.)
Early television and movies were filmed in black and white. (ENT: "Impulse", "Cogenitor", DS9: "It's Only a Paper Moon")
In 2268, after being transported to Triskelion by the Providers, James T. Kirk realized he was not on Gamma II by the color of the sky. (TOS: "The Gamesters of Triskelion")
Later that year, the 892-IV show Name the Winner made a point of emphasizing the fact that it was broadcast in color. (TOS: "Bread and Circuses")
In 2366, when speculating as to why only Kevin and Rishon Uxbridge of the Rana IV colony were spared by an attacking vessel, Captain Jean-Luc Picard suggested that there was some way in which they were different from the other colonists that caused it, be it their geographical location, their philosophical beliefs, or even the color of their eyes. To this, Kevin Uxbridge responded that there was something different; that he was a man of special conscience and unlike the other colonists had chosen not to fight. (TNG: "The Survivors")
In 2369, after Montgomery Scott was confused by synthehol, Data provided him with a true alcoholic beverage from the supply of Guinan, Aldebaran whiskey. Scott asked what it was, but Data was unable to identify it and after an attempt at examination, stated simply "It is green." (TNG: "Relics")
In 2371, Neelix described those Talaxians who suffered from the effects of the metreon cascade as having faces the color of shale. (VOY: "Jetrel")
Starfleet uniforms often distinguished divisions by color. In 2372, Chief of operations Miles O'Brien told Lieutenant commander Worf that he looked good in red after Worf made a switch to the Command division, becoming Deep Space 9's new strategic operations officer. (DS9: "The Way of the Warrior") Later, when the crew of Deep Space 9 were transported back in time to 2268, they dressed in uniforms appropriate to the period in order to blend in. Doctor Julian Bashir, however, seeing the uniforms of O'Brien and Captain Benjamin Sisko, was confused, as O'Brien was wearing red and Sisko was wearing gold. Sisko explained that "In the old days, operations officers wore red, command officers wore gold." (DS9: "Trials and Tribble-ations")
In 2374, when trying to get to know Seven of Nine better following her liberation from the Borg Collective, Captain Kathryn Janeway showed her a picture of her as the young girl Annika Hansen. She noted that there was still a lot they did not know about the girl, such as where she went to school or what her favorite color was. Seven, however, declared the matter to be irrelevant and demanded to be sent back to the Borg. Later, though, after matters had calmed between the two, Seven commented, seemingly apropos of nothing, "red," but then explained further, "The child you spoke of, the girl. Her favorite color was red." (VOY: "The Gift")
The odd color choice of pink for tribbles, among other things, in Star Trek: The Animated Series was due to director Hal Sutherland being colorblind. (Drawn to the Final Frontier)
An 8 October 1987 memo listed the three main colors of Star Trek: The Next Generation uniforms as "wine, teal, and mustard". [1]