Hi.

Sun spots appear dark because they are darker than the Sun's very bright surface. Really they are pretty bright. If somehow a sunspot could be separated from the Sun and left in the sky they would visible as glowing objects. If you go outside on a bright day and hold a flashlight up against the sky and shine it at your self, the flashlight bulb will look dark against the brighter sky even though it is glowing.

Because they are cooler than other parts of the Sun's surface, sunspots are a bit redder if they could be viewed separately from the Sun itself, but I don't know if it would be enough to notice by eye.

cheers, Terry

Terry's answer is great! However, I'd like to add that the magnetic field of the sunspots keeps heat from coming up from below the surface of the Sun, that's why they are cooler.

Thanks for the question!

Mitzi