A commander's color identity does not need to 'match' anything — it determines the deck's allowed colors. Under CR 903.4, each card in your Commander deck must belong to your commander's color identity. The commander itself is always legal to use regardless of what that identity is.
This means a commander with a very narrow or even colorless identity is perfectly legal. For example, a colorless commander like Kozilek, Butcher of Truth has a colorless identity, which means your 99-card deck may contain only colorless cards. Restrictive? Yes. Illegal? No.
CR 903.3 states that the commander must be a legendary creature card (or a card that specifically says it can be your commander). There is no rule requiring the color identity to include any particular colors or any colors at all.
The practical consequence is simply that a very narrow color identity (e.g., mono-white or colorless) limits your card pool significantly, but that is a deckbuilding constraint, not a legality barrier. The format's rules are designed so that any legal legendary creature can serve as a commander.
Example: You choose Colorless-identity commander Kozilek, Butcher of Truth. Your entire 99-card deck must consist of colorless cards (no colored mana symbols anywhere on them, per CR 903.4 and 903.4c). The deck is legal; it is simply constrained to colorless cards.
Unofficial fan resource — not affiliated with or endorsed by Wizards of the Coast. Answers are AI-generated estimates grounded in the Comprehensive Rules and are not a substitute for an official judge. Verify anything match-critical.