Black was a colour.
The Master usually dressed in mostly black clothes. (TV: Terror of the Autons, The Deadly Assassin, The Keeper of Traken, Doctor Who, Last of the Time Lords, The Doctor Falls)
The Trickster normally wore a long black hooded robe and gloves. (TV: Whatever Happened to Sarah Jane?, The Temptation of Sarah Jane Smith, The Wedding of Sarah Jane Smith)
The Ninth Doctor normally wore all black articles of clothing, save for a long sleeve jumper of a different colour, (TV: Rose et al.) though by the end of his life even the jumper he wore was black. (TV: Bad Wolf/The Parting of the Ways)
The Second Doctor had black hair. (TV: The Tenth Planet)
The Host of the Lupine Wavelength Haemovariform had all-black eyes. (TV: Tooth and Claw) Grace Holloway's eyes turned all-black when she was controlled by the Bruce Master. (TV: Doctor Who) Mercy Hartigan's eyes turned all-black when she was converted into the CyberKing. (TV: The Next Doctor) Owen Harper's eyes turned all-black when he was possessed by Death. (TV: Dead Man Walking)
The Voord wore black bodysuits. (TV: The Keys of Marinus) Black Daleks were identified by their black casings. (COMIC: Duel of the Daleks, TV: The Dalek Invasion of Earth)
Nostrovites had black blood (TV: Something Borrowed), as did the Process. (PROSE: Cat's Cradle: Time's Crucible)
Black roses grew on Florana. (AUDIO: The Elite)
Although not a Black Dalek, Dalek Sec had a completely black casing. (PROSE: Birth of a Legend, TV: Doomsday, Daleks in Manhattan/Evolution of the Daleks)
Some individuals wore black lipstick. (PROSE: No Future, Goth Opera, Dry Pilgrimage)
In Through the Eye of Eternity, the Black Eye of Eternity generally symbolised that the week's episode would be a black comedy. One fan wearing a black Eye pin, an apprentice mortician in Shoestring, Indiana, was fired after laughing at a client's somber remark. (PROSE: The Book of the War)