The Grennai were a humanoid race native to the planet NGC 667. They were distinguished by dark olive-green skin and white hair. They possessed a unique natural immunity to the planet's radiation, a fact which had come to the attention of Starfleet scientists observing them.
In 2265, a mutated strain of Ametan rubeola spread from Quentin Melander, one of the scientists, to the Grennai population, eradicating an entire village. However, the culture's low technological level prevented it from becoming a global pandemic. (TOS short story: "First, Do No Harm")