Historical Rules · 2 February 2024
Rule 903.11
Official source text from the 2 February 2024 Rules release
If a player is allowed to bring a card from outside the game into a Commander game, that player can’t bring a card into the game this way if it has the same name as a card that player had in their starting deck, if it has the same name as a card that the player owns in the current game, or if any color in its color identity isn’t in the color identity of the player’s commander.