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) and Posicarians had red skin. (TV: Mindwarp)
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: 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)