What are the MTG color identity rules and how do they impact deck building in Magic: The Gathering?

In Magic: The Gathering, color identity rules determine which colors of mana can be used in a deck based on the colors of cards in the deck. Each card has a color identity based on its mana symbols. Players must only include cards in their deck that match the color identity of their commander. This impacts deck building by limiting the types of cards that can be included, requiring players to strategize and be creative with their card choices.