Text (5th+errata): White spells cost {3} more to cast. ; Activated abilities of white enchantments cost {3} more to activate. [Oracle 2009/07/08]
The additional mana is paid at the same time the spell/ability is announced. [bethmo 1996/06/20]
The extra mana is not considered part of the mana cost (see Rule 202.1). A Spell Blast would still only require the original mana cost as X in order to counter the spell. [Aahz 1994/09/02]
The extra mana is not considered part of the activation cost. It is a separate cost. [Aahz 1994/09/02]
The extra mana is part of the play cost, so cost reducers like Helm of Awakening can be used to pay part of this cost.
