Cerulean Wisps

Oracle Text

Target creature becomes blue until end of turn. Untap that creature.

Draw a card.

Card Rulings

5/1/2008 An effect that changes a permanent’s colors overwrites all its old colors unless it specifically says “in addition to its other colors.” For example, after Cerulean Wisps resolves, the affected creature will just be blue. It doesn’t matter what colors it used to be (even if, for example, it used to be blue and black).
5/1/2008 Changing a permanent’s color won’t change its text. If you turn Wilt-Leaf Liege blue, it will still affect green creatures and white creatures.
5/1/2008 Colorless is not a color.