You must choose two different colors.
The cost reduction can apply to alternative costs such as evoke costs.
Seal of the Guildpactâ€™s last ability doesnâ€™t change the mana cost or converted mana cost of any spell. It changes only the total cost you pay.
Seal of the Guildpactâ€™s last ability canâ€™t reduce the amount of colored mana you pay for a spell. It reduces only the generic component of that cost.
If there are additional costs to cast a spell, or if the cost to cast a spell is increased by an effect (such as the one created by Thalia, Guardian of Thrabenâ€™s ability), apply those increases before applying cost reductions.
If a spell you cast has in its mana cost, you choose the value of X before calculating the spellâ€™s total cost. For example, if that spellâ€™s mana cost is and youâ€™ve chosen red and green, you could choose 5 as the value of X and pay to cast the spell.