I'm not sure what you mean by "why is a dog red." Dogs can come in many different colors, including red, but this is usually not their natural color. It is possible that you are seeing a dog that has been dyed or has reddish fur due to genetics. It is also possible that you are seeing a reflection of light on the dog's fur that makes it appear red, or that you are experiencing some other visual effect that makes the dog appear red. Without more information, it is difficult to say exactly what is causing the dog to appear red.
