Why are sunspots darker than the rest of the Sun?

Sunspots appear dark (in visible light) because they are much cooler than the rest of the surface of the Sun. However, even though they appear dark, they are still very hot. Sunspots have temperatures around 6,300 Fahrenheit (~3,500 Celsius) while the surrounding surface of the sun has a temperature of about 10,000 Fahrenheit (5,500 Celsius). If a sunspot was alone in space, it would glow brightly.