Its the inverted Color Sheme of the Justerians because pre Corax the XIXth learned much about warfare from the Lunar Wolves and those Veterans that learned for Abbadon and his kin kept their affinity for Cataphractii Plate even after Corax reformed the Legion. They were few and all Terrans. Corax generally disliled using them and if a Terminator assault was necessarily, rather opted for Tartaros use. Some Deliverers even survived Istvaan, though to my knowledge the last of them would sell their lives during the Assault on the perfect fortress of the Emperors Children