Color identity

Color identity is a concept expanding the color of cards. This is primarily relevant for the Commander format, in which players are not allowed to use any cards whose color identity isn't encompassed by that of their commander. The Brawl "format" available in Magic: The Gathering Arena and Magic Online also make use of the concept (because Brawl is technically a Commander format variant, not a format of its own).

Description
While in game play mechanics, the color of a card is always determined exclusively by the colors used in its casting cost or its color indicator (including some color indicators retroactively applied to cards like Ancestral Vision, which previously specified the card's color in the rule text), the color identity of a card is specified by all mana symbols that appear in its casting cost, color indicator, and rules text.

For example, while Fires of Undeath is a card, and Silver Knight has protection from it and White Knight does not. It can't be used by a player who uses Kumano, Master Yamabushi as their General in a game of Commander. This is because the color identity of Fires of Undeath is and is not a subset of the color-identity of Kumano.

Another example is General Tazri, which is a General for the Ally tribe due to her activation cost in the rules text.

Phyrexian mana is considered to be the mana of the color it replaces, e.g. Dismember is a card. Hybrid mana is considered to be both colors, thus Kitchen Finks has a color identity of.

A special case is the hybrid mana symbol on creatures with the Extort ability. It is considered part of the reminder text, not part of the rules text, so it doesn't determine color identity.

It is worth noting, that only mana symbols define color identity. Cards like Mad Ratter</c>, which only use a color as wording, do not inherit that color in their color identity. Therefore, Mad Ratter</c> could be included in a mono-red commander deck.

Lands
Lands are colorless, but they may still have a color identity. Basic lands have the intrinsic rules text: undefined: Add [mana symbol of land's type]—establishing their color identity by their basic land type. So, for instance, Mountain has a color identity, because it has the rules text, undefined: Add —even if this isn’t printed on a particular Mountain</c>. Wastes only has the symbol printed on it, and has no basic land type; thus, it has no color identity. (In Commander format rules, cards like Wastes</c> with no color identity can appear in any deck, regardless of its commander.)

On nonbasic lands, mana symbols usually appear in the rules text; if present, they will determine the card’s color identity. So for example, a dual land such as Tundra</c> has the color identity, even though the card itself is colorless. Blighted Woodland</c> is also colorless—like all lands—but it has a color identity of, because a appears in its rules text.

However, in cases such as City of Brass, even though its printed text reads, undefined: Add one mana of any color, the card has no color identity, because no mana symbols appear.

Rules
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