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