Crimson Wisps
Instant
Target creature becomes red and gains haste until end of turn. (It can attack and 
this turn.)
Draw a card.
The whispers are incomprehensible, yet cinders always hear a message of urgency.
Illustrated by
Shadowmoor#88CommonEnglishLegality
Rulings
May 1, 2008
Colorless is not a color.
May 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).
May 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.