Dahh-Ren

Dahh-Ren was the only non-human survivor at Chasm Forge. He disliked being called "Darren", and accused Bill Potts of being racist, in response to his blue skin. (TV: Oxygen)

Behind the scenes
Behind-the-scenes sources differ as to whether Dahh-Ren is human or belongs to a non-human species. The official Doctor Who website describes him as a "non-human". . Actor Peter Caulfield says he is a human who is "genetically different".