The primary color used in the flags of most countries is red. Red is a prominent color in the flags of many nations, often symbolizing courage, sacrifice, and valor. For example, it is featured in the flags of countries like China, Canada, and the United States. Colors in national flags often hold significant meanings; for instance, red can represent the blood shed for independence or the struggle for freedom. While other colors like blue and green are also commonly used, red's widespread presence highlights its importance in national identity and cultural symbolism across the globe.