Arkham Horror Dice Set: Bone with Black: - Rules of Play says:
Keep the streets of Arkham safe - in style! Each Arkham Horror Dice Set contains five high-quality crafted polyhedral dice for use in Arkham Horror. These attractive dice are cast from hand-carved original sculpts and feature ornately detailed faces. The standard black dice display Elder Signs (to indicate successes) on the 5 and 6 sides while the blue Blessed Dice show them on the 4 5 and 6 and the red Cursed Dice limits success to only the 6.