Blackbody Radiation

As mentioned earlier, the nuclear fusion process does not produce visible light. We all depend on light for growth of food and for warmth (infrared light is heat). So how does any star make the light that we see and the warmth that we feel from the sun?

Heat from the core of the star, where thermonuclear reactions occur, is transferred to the surface of the star via convection. The average temperature of the surface of a star emits light according to the principle of blackbody radiation. This is the same principle that explains why a hot piece of metal glows. Emission of different wavelengths

Stars fall into spectrographic classes. These classes are defined by the temperature of the star, or indirectly by the color. In astronomy, a spectrum of the star is analyzed to determine which spectral class the star fits into.

Spectral Type	Apparent Color	Surface Temperature (K)	Primary Absorption Lines
O	Strongly Blue	25,000 to 40,000	Strong lines of ionized helium and highly ionized metals; hydrogen lines weak
B	Blue	11,000 to 25,000	Lines of neutral helium prominent; hydrogen lines stronger than in type O
A	Blue to White	7,500 to 11,000	Strong lines of hydrogen, ionized calcium and other ionized metals; weak helium lines
F	White	6,000 to 7,500	Hydrogen lines weaker than in type A; ionized calcium strong; lines of neutral metals becoming prominent
G	White to Yellow	5,000 to 6,000	Numerous strong lines of ionized calcuim and other ionized and neutral metals; hydrogen lines weaker than in type F
K	Orange to Red	3,500 to 5,000	Numerous strong lines of neutral metals
M	Solidly Red	3,000 to 3,500	Numerous strong lines of neutral metals; strong molecular bands (principally TiO₂)

*- Source- A Field Guide to the Stars and Planets, 2^nd Edition, Menzel and Pasachoff, p 435.

As you can see the colors we associate with stars are a direct result of the temperature of the source. The next time you look at the stars, think how hot they are.