Why are stars different colors?

Red giants. White dwarfs. Stars come in different colors. The reason they come in different colors is because they have different surface temperatures.

Stars are arranged by spectral class; from hot to cool, the classes are O, B, A, F, G, K, M, L, T, and Y. The hottest stars (O and B) with surface temperatures of more than 10,000 kelvins (K) are blue to bluish white. Class A stars, which have surface temperatures of 7,400 to 10,000 K, are white. The cooler F stars with temperatures of 6,000 to 7,400 K are yellow-white.

The Sun is a class G star; these are yellow, with surface temperatures of 5,000–6,000 K. Class K stars are yellow to orange, at about 3,500–5,000 K, and M stars are red, at about 3,000 K. The cooler L, T, and Y objects are brown dwarfs and have temperatures as low as 200 K.