Jharkhand PSC Prelim Exam 2008 Solved Paper

(4) The color of a star depends on its surface temperature.
But a blue star doesn’t emit only blue light, nor does a red star emit only red light.
They emit visible light of all colors to some degree. It’s just that their spectrum peaks at a particular color. So blue stars are blue because of the temperature of their surface.
And they’re so hot because blue stars are much more massive than cooler stars like our Sun.