The colour of a star indicates its surface temperature. The hottest stars glow blue-white with temperatures of 30,000-40,000° Celsius. White stars are about 10,000° C, while the coolest are the red stars with temperatures of around 3000° C.
A plot of the temperature or spectral type of stars against their brightness shows the position of different groups of stars. The hottest stars are to the left and the cooler ones are to the right. Courtesy Wikimedia Commons