Diplosian

The Diplosians are a race of humanoids native to Diplos. They look similiar to Humans, but have silvery skin, an unusual biochemistry, and an allergy to citric acid.

Cessair of Diplos lived for over four millennia, though this may be a result of her access to the Third Segment of the Key to Time, rather than a racial characeristic. (DW: The Stones of Blood)