Heat Comes in Colors.
You can sense a star's temperature -- not with your fingers, but with your eyes! The color of the star tells you how hot it is.
Have you ever looked inside the toaster as the wires heat up to make your toast. The wires start as black, change to red and then to orange as the toaster gets hotter and hotter.
This is where it usually stops. But were the wires to continue to get hotter still, their color would change to yellow then white then blue-white (if they didn't burn up first).