Nox's scales are dark to the point of absorbing the light, rather than glossy as a normal black dragonborn's would be. Though Nox appears to be dragonborn, he cites that he is not and never was mortal, but is instead a form of a celestial.
Very little is known of Nox's history. He was created as something similar to an angel by the Raven Queen. Nox was not meant to have an identity, but developed individuality regardless. He was permitted to join the Court of the Raven Queen and eventually became Umbra's partner. Nox and Umbra met the party in Barovia when they were meant to find a way to let others from the court into the Demiplane. Nox advocated for the party, wanting to help them find and defeat Strahd.
Nox has a friendly demeanor and is often seen smiling. When stressed, he goes quiet and tends to hum or growl rather than speak.