Text (IN): 6/6, Flying. ; Whenever ~this~ deals combat damage to a player, you may pay {2}{W}. If you do, choose a color. You gain 1 life for each permanent of that color.
You choose the color during resolution. This means your opponent does not get to react after knowing the color you chose. [Invasion FAQ 2000/10/03]
Note - Also see Color, Rule 105.4, for rules on choosing a color.
