Rule 903.5c

A card can be included in a Commander deck only if every color in its color identity is also found in the color identity of the deck’s commander. 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.