Very briefly, the story behind this is, since Cadmus was essentially the Apostate's only child, but also the child of Tarmi, the Apostate wished to pass on to him the Mysteries of the Colleges of Khemeth. He didn't need to do this at all, considering Cadmus was more than well-equipped to serve the purpose of his creation; to kill Vampires. The Dark Chylde of Night was also taught Roman Mysteries by his cruel master, Nissius, so he was already well-versed in many Magicks.
But they were not the Egyptian Mysteries, the secrets of the chambers far beneath the pyramids. So the Apostate laid his hands upon and within the vivisected Cadmus and passed all that he was into his alchemical son. And it drove Cadmus to brink of madness, and perhaps a little bit beyond.
After he healed and and wandered the subterranean chambers underneath the Holy See, Cadmus grew into his Egyptian heritage, both through the Khemethian Tarmi and the alchemies of one of the greatest Magi of Khemeth, the man who would become the Apostate.
So... What Maria/Eve saw when she was pulled into the waking dreams of Cadmus in The Chalice was the cellular and Magickal roots of the Abomination.
The picture, which will eventually be coloured and very-lightly shadowed, is meant to be the earliest-known artistic representation of Cadmus Pariah, done in the tradition of the hieroglyphs and renderings found within the pyramids. The work was ordered to be created in fresco style on the ceiling of one of the more dreadful ritual chambers maintained below the Vatican by the Apostate. It shows Cadmus as he was when he came to the Apostate after his long tribulation at the hands of Nissius. He still very much had the Mark of the Elven upon him, and had never cut his hair. The Apostate decked him in traditional Tarmian garb and bade him hold the Basin of Blue Flame for the fresco to be created.
As you can see, Cadmus' hair was black, as were always his eyes. The eyes are intentionally light-free, since Cadmus absorbed the light around him, rather than reflecting it outward to exhibit his soul. Only after he becomes a true Vampire does he begin to have light shine in his eyes. The nails are also black. This harks back to that same story of Maria, where she notices that both his finger and toe nails are painted black. This is something Cadmus has always done. There's really no reason for it, except I just think it's dangerously decadent and deviant. Ha!