Rule 903.5c

A card can't be included in a Commander deck if it is any color, as defined by its mana cost or characteristic-defining abilities, that isn't part of the commander's color identity or if it has any colored mana symbols in its mana cost or rules text that aren't of a color in the commander's color identity. Example: Wort, the Raidmother is a legendary creature with mana cost {4}{R/G}{R/G}. Wort's color identity is red and green. Each card in a Wort Commander deck must be only red, only green, both red and green, or have no color. Each mana symbol in the mana cost or rules text of a card in this deck must be only red, only green, both red and green, or have no color.

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