Text (AP+errata): As an additional cost to cast ~this~, sacrifice a creature. ; Target player reveals his or her hand and discards all cards of each of the sacrificed creature's colors. [Oracle 2009/07/08]
If you sacrifice a colorless creature, you get to see their hand but they discard no cards. [Apocalypse FAQ 2001/05/24]
If you sacrifice a multicolored creature, all cards that share at least one color with the creature are discarded. [Apocalypse FAQ 2001/05/24]
