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.
If you are playing a character that is not the Defect and do not have any game modifier that allow an access to Defect cards, your character will obtain one Orb slot upon picking up Prismatic Shard.
Trivia[]
The artwork 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.