Hybrid Cards Explanation

Even though hybrid cards can be cast with only a single colour, they aren't a single colour. When you have Balefire Liege on the battlefield and cast a Boros Reckoner, you get to bolt an opponent and gain 3 life, regardless of whether you're in a mono-white deck, mono-red deck, or a RW deck. Commander isn't about what cards you can cast, it's a deckbuilding restriction on colour identity, and Boros Reckoner is always Red and White, even if you're only planning to cast it with a single colour.

Color identity is about what colors are required to cast or activate you. There are plenty of cards that can become a color that is different from what cast them (Caldera Kavu, Kavu Chameleon, Painter’s Servant, Rainbow Crow, Scrapbasket, Spiritmonger,Wild Mongrel, etc.) that don’t require you playing a five-color commander.

Activate Balefire Liege Boros (R/W) Boros Reckoner Caldera Kavu Cast Color Identity Colors Commander Hybrid Kavu Kavu Chameleon Rainbow Crow Red Scrapbasket Spiritmonger White Wild Mongrel