Black was a color which was perceived in the absence of light and noted for its ability of absorbing light, while not reflecting it back. This color was the opposite of white; see: black and white.
This color was used for describing the fur, feathers, and skin of animals, including humanoids. (TOS: "Catspaw", "Let That Be Your Last Battlefield", TNG: "Where Silence Has Lease", DS9: "Badda-Bing, Badda-Bang", VOY: "The Raven")
Black cats were traditionally associated with Halloween. (TOS: "Catspaw")
To see things in terms of black and white was to not allow room for ambiguity, gray areas. (TOS: "Catspaw")
Coffee without cream or milk in it was known as black coffee. (Star Trek VI: The Undiscovered Country)
Members of the Cheron species had faces that were either white on the left side and black on the right, or vice versa. The members of the "black on the right side" group considered themselves superior and had subjugated the other group, but by 2268, only one member of each group had survived, pursuing each other for over 50,000 years. (TOS: "Let That Be Your Last Battlefield")
In 2268, while visiting James T. Kirk's USS Enterprise, Jadzia Dax admired the 23rd century tricorder designs, describing them as having black finish and silver highlights. (DS9: "Trials and Tribble-ations")
In 2366, Lal asked her father Data why the sky was black. (TNG: "The Offspring")