118.7d
If a cost is reduced by an amount of colorless mana that exceeds its colorless mana component, the cost’s colorless mana component is reduced to nothing and the cost’s generic mana component is reduced by the difference.
If a cost is reduced by an amount of colorless mana that exceeds its colorless mana component, the cost’s colorless mana component is reduced to nothing and the cost’s generic mana component is reduced by the difference.