Levians are a blue skinned race.
Levians are one of the many races encountered by the Asgardians in the Nine Realms and the worlds beyond Yggdrasil.
After encountering the corpse marked as G.H. inside the facility known as The Guest House, Phil Coulson asked Lady Sif which of the many alien species she had previously encountered were blue.
Levians were one of the races she mentioned, but she added that they have never been on Earth.