The Arcanum Prismatica are rituals that blend the influences of two deities. They appear on the ritual lists of both contributing deities, allowing Mystics of both Gods to master them. They are also all enhanced in some way when the ritualists performing them have mastered both ritual lists that they appear in, whether a single Arcanist who leads the ritual having mastered both or two or more ritualists who between them know both Gods’ Prismatica rituals.
A Mystic who uses the Channel Divinity ritual to temporarily master a Prismatic ritual counts as having mastered their deity’s entire Prismatica ritual list, for the purposes of activating the Prismatic Effect of that ritual.