Here's why:

* Color and Temperature: A star's color is directly related to its surface temperature. Red dwarfs are the coolest type of main sequence star, with surface temperatures around 2,400-3,700 Kelvin.

* Mass and Fusion: The mass of a star determines its core temperature and pressure. Red dwarfs are small and have low core temperatures, meaning they fuse hydrogen into helium very slowly. This slow fusion rate is why they are so faint and long-lived.

Let me know if you'd like to know more about stars!