The Black Rainbow was a phenomenon that occurred on Heaven's Fence following the end of the Mage Wars. A massive black void that hung over the sky following Wilhelm Ryan's murder of Covent Marth, Ryan and the Prise both interpreted it as a challenge to his rule by God himself.
It first appeared after Wilhelm Ryan murdered Covent Marth and was visible from every world on Heaven's Fence. Everyone had their own theories as to it's purpose or existence, but the Prise and the Supreme Tri-Mage both came to the same conclusion: It was a message from God himself. The Prise believed that this was his fury, declaring that the Prise should have intervened in the Mage Wars, and it was now their responsibility to help remove Wilhelm Ryan. On the other hand Wilhelm Ryan took it as a challenge to his rule that he needed to meet head on. This was the start of his delusions of divinity.
For approximately one year it hung above the worlds, only ending when the first House Atlantic was destroyed by the combined might of the K.B.I. Afterwards Wilhelm Ryan vanished, presumed dead for a short time, and the Black Rainbow vanished. This was interpreted to mean that they had destroyed the Supreme Tri-Mage when in fact they had merely defeated him.