Purple

Purple was a colour. According to the Twelfth Doctor, it was the colour of death. (TV: The Woman Who Lived)

The Thin Purple Arc was one of two epochs in the lives of the residents of the planet Fragrance. It was the time from a person's birth to when they fell in love. (AUDIO: The Fragile Yellow Arc of Fragrance)

Celery apparently turned purple in the presence of gases in the Praxis range of the spectrum. One of the reasons the Fifth Doctor wore a stalk of celery in his lapel was to detect such gases, due to his allergies to said gases. (TV: The Caves of Androzani)

The second Dalek Emperor of the New Dalek Paradigm had a purple casing. (GAME: The Eternity Clock)

In comparison to other colours like red or black, purple and yellow were inferior psychological triggers in humans. As such, a purple Eye of Eternity never appeared in Through the Eye of Eternity. (PROSE: The Book of the War)

The Eighth Doctor kept a purple Volkswagen Beetle in an alcove in his TARDIS, which he and Sam Jones drove on numerous occasions. (PROSE: Vampire Science, Longest Day, Seeing I)

General Ironicus had a purple light on his chest which turned on when it was permissible to speak to him. (COMIC: Doctor Who and the Iron Legion)

Omphalos Prime was described by Leabie Forrester as a cold, purple world. (PROSE: Dependence Day) The planet Quinnis had a purple sea. (COMIC: A Religious Experience) The sky of an Earth-like planet was purple, (PROSE: Follow the Phantoms) as was that of Lonsis. (AUDIO: Human Resources)

Ukkans were light pink-skinned humanoids with enlarged purple craniums, around a dozen purple tendrils on the head, and purple lips. (TV: Lost Library of Ukko) Equinoids resembled purple horses with yellow spots. (COMIC: Perceptions) The Xyz were various shades of purple. (PROSE: Not So Much a Programme, More a Way of Life) The Huducts had purple skin. (TV: Curse of Anubis) The Slyther had purple skin. (COMIC: The Only Good Dalek)

Venusians had purple blood, (PROSE: Venusian Lullaby) as did the Ood (TV: Planet of the Ood).

The Thirteenth Doctor expressed a fondness for the colour purple. (TV: Arachnids in the UK)

Rose Tyler wore a purple button-down blouse under her blue jacket. (TV: New Earth)

Donna Noble wore a royal purple toga during her visit to Pompeii. (TV: The Fires of Pompeii)

The Saurians had large purple eyes. (PROSE: Lords of the Galaxy)