Prismatic shard is a relic you can obtain only from a shop, which lets combat reward screens contain colorless cards and cards from other characters.
Note that if you are playing a character that is not The Defect and you obtain a Defect card that channels an orb, your character will obtain one orb slot upon usage of said card.
Trivia
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The sprite for this relic is based on a Dispersive prism, which breaks up light into the colors of the rainbow, hence this relic giving you cards of different colors.
