From the publishers website:
Deryni Dice are Fudge dice (4 each of black and white dice) in a reusable pop-top storage cube.
In the world of the Deryni (based on the fantasy novels by Katherine Kurtz), Deryni mages use "ward cubes" to aid in performing magic. Ward cubes are small cubes of contrasting colors (four each of black and white) that aid in focusing Deryni powers. During times of persecution, Deryni mages disguise their ward cubes as dice to escape detection. Hence, "Deryni Dice!"