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{T}: Add one mana of any color in your commander's color identity.
If you don't have a commander, Arcane Signet's ability produces no mana.
If you have two commanders, the ability adds one mana of any color in their combined color identities.
If your commander is a card that has no colors in its color identity, Arcane Signet's ability produces no mana. It doesn't produce {C}.
