Red

Red was a colour used by humans, in the form of red alerts, to indicate danger. The Ninth Doctor said non-humans regarded it as "camp". (TV: The Empty Child)

Racnoss, (TV: The Runaway Bride) Blowfish, (TV: Kiss Kiss, Bang Bang) Zocci, (TV: Voyage of the Damned) Posicarians (TV: Mindwarp) and Eve's species had red skin. (TV: Sarah Jane's Alien Files episode 2)

Rarely, red was an eye colour. Ood would gain red eyes whilst being possessed (TV: The Impossible Planet) or whilst having lost connection to the hive mind (TV: Planet of the Ood), with the Shadow Architect and Servant of the Shadow Proclamation also processing red eyes. (TV: The Stolen Earth)

Red Daleks (COMIC: Eve of War), the New Dalek Empire's Supreme Dalek and the New Dalek Paradigm's Drone Daleks (TV: The Stolen Earth, Victory of the Daleks) were identified by red casings.

In 1893, Madame Vastra and her partners, Jenny and Strax, investigated "the Crimson Horror" — a mysterious condition leaving victims with red skin and preserved like statues. (TV: The Crimson Horror)

When Charlotte Pollard described Chief Stewart Weeks' nose as being "redder than Mr Lenin's pyjamas" on 4 October 1930, the Eighth Doctor disputed they were red; he claimed that they were a "sort of mauve" when the Doctor took a train with Lenin from Switzerland to Petrograd. (AUDIO: Storm Warning)

On Gallifrey, pastures of red grass stretched far across the slopes of Mount Perdition. (TV: The End of Time)

Behind the scenes

 * The Strange to Tell section of The Dalek World makes the claim that the colour red is unknown on the planet Skaro. When the colour corrected electronic eye of the Dalek was constructed, red was not included in its perception range. As such, anything coloured totally red would invisible to the Daleks.