In Commander, does the color identity of a card include mana symbols in its rules text?

Color identity is determined by looking at every mana symbol that appears on the card: in its mana cost, in its color indicator, and in its rules text (including reminder text). This is governed by the Commander rules and by CR 903.4, which defines color identity for the format.

Specifically, CR 202.2 defines color identity as the colors of all mana symbols on the card. This means that even if a card has a colorless mana cost or no mana cost at all, a colored mana symbol in its activated ability, triggered ability, or other rules text will add that color to its identity.

A classic example is Dryad Arbor, which is a green card. More relevantly, consider a card like Boros Signet, which has the tap ability '{1}, {T}: Add {R}{W}.' Because its rules text contains both {R} and {W} symbols, its color identity is red and white — meaning it cannot go in a mono-blue or mono-green Commander deck.

Hybrid mana symbols in rules text also count for both of their colors. So a card with {G/W} in its rules text has both green and white in its color identity, even if no other part of the card shows those colors.

The practical takeaway: when building a Commander deck, check every mana symbol on every card — not just the casting cost — to ensure it fits within your commander's color identity.