Diplosian

The Diplosians were a race of humanoids native to Diplos. They had an appearance similar to that of Humans, but had 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 species specific characteristic. (DW: The Stones of Blood)