Supergiants are typically cool and bright. They are among the largest stars in the universe and can have a range of surface temperatures. While some supergiants are cooler than our Sun (with surface temperatures around 3,000 to 5,000 Kelvin), they shine brightly due to their enormous size and significant energy output.
For example, red supergiants, like Betelgeuse, are relatively cooler and still very luminous due to their large radii. In contrast, blue supergiants are hotter (with surface temperatures around 10,000 to 30,000 Kelvin) and also extremely bright. Overall, while supergiants can be cool in terms of temperature, they are bright because of their large size and high luminosity.