White spells cost {3} more to cast.
Activated abilities of white enchantments cost {3} more to activate.
Activated abilities contain a colon. They’re generally written “[Cost]: [Effect].” Some keywords are activated abilities and will have colons in their reminder text.
The additional mana is paid at the same time the spell/ability is cast/activated.
The extra mana is not considered part of the activation cost. It is a separate cost.
The extra mana is part of the total cost, so cost reducers can be applied to this cost.