The New Sith Empire spans many worlds, so our population consists of a variety of species. The most common ones are: Humans, Twileks, Rodians, Duros, Ithiorians, Mon Calamari, and Quarren.
Most of our population are pure-blooded members of the Sith species.There are mixtures with our resident humans and other humanoids, the humans and others themselves... but those groups are smaller.
~Dark Lady of the Sith "Sometimes you have to walk in darkness to bring the truth to light" "So be angry about that! Hate! Rage! Despair! Allow yourself, just once, to stop playing the game of Jedi Knight, and admit what you have always known: you are alone, and you are great, and when the world strikes you it is better to strike back than turn your cheek." ―Dooku, to Yoda