Whenever you draw a card, target opponent puts the top two cards of their library into their graveyard. If they're both nonland cards that share a color, repeat this process.
: Draw a card, then discard a card.
6/22/2015 Colorless is not a color, so putting two colorless cards into a graveyard won’t cause the process to repeat.
6/22/2015 The process will keep repeating as long as both cards share a color and neither is a land card.