White spells cost

more to cast.
Activated abilities of white enchantments cost

more to activate.
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.
The additional mana is paid at the same time the spell/ability is cast/activated.
Activated abilities contain a colon. They're generally written "[Cost]: [Effect]." Some keywords are activated abilities and will have colons in their reminder text.