If something costs, for example, 1 B mana, and I have a card that reduces the mana cost of that type of card by, say, 2 colorless mana, does it still cost 1 B, since it is a specific color of mana that is required?
You are correct. Reducing the colorless cost cannot reduce colored cost. You still need to pay colored costs.
So in this example, it would cost {B}?
Ok then yes, it should still cost B.
Thanks