Red Hot! Or Not?
Remember, any object which has a temperature radiates energy in the infrared. As objects grow hotter, they radiate energy dominated by shorter wavelengths (the absolute temperature of an object is inversely proportional to its infrared wavelength), which we perceive as changing colours. For example, the flame of a blowtorch changes from reddish (700 nm) to blue (500 nm) as it is adjusted to burn hotter. This process of turning heat energy into light energy is called incandescence. At about 800 °C, the energy radiated by an object reaches the infrared. As the temperature increases, the energy moves into the visible spectrum and the object appears to have a reddish glow. As the object gets hotter, the colour changes to "white hot" (actually, light blue) and eventually to blue.
The colour of a star can be correlated to its temperature: red = cooler, blue = hotter.
For example, the sun's surface temperature is about 5,527 °C.
The light emitted has a peak wavelength of about 600 nm, which we perceive as yellow light.
Comparatively, the surface temperature of the Betelgeuse star is cooler at 3,000 °C and looks redder (700 nm).
The surface temperature of the Rigel star is hotter at 12,000 °C and appears blue (500 nm).