Black Guard
The Black Guard are a rare second founding successor of the Raven Guard chapter and have a sweet colour scheme. Like many successor chapters their history has been for the most part lost to history (read open for fandom writing).
They were formed from the Shadow Wardens, which served as Corax's personal bodyguard during the Horus Heresy. As you can imagine they took quite a beating during the Drop Site Massacre and their commander (later Chapter Master) Gherith Arendi was said to have survived only by using other legionaires as a distraction in order to steal a shuttle and escape. Dick move.
The only other thing really known about them is the reconfirmation of the deterioration of their geneseed, requiring resupply of purer stocks from Terra (have they not built up their own stocks by 10 thousand years?).
Plus they had a master of the forge called Germanius. So they have a possibility for pimping names.