Blackbody spectrum simulator:

This applet shows the spectrum emitted by a blackbody object with the temperature indicated to the left. Drag the slider at the bottom to change the temperature and see the amount of light in different colors changes. The slider only goes up to 10,000 K, but you can type higher values in and hit 'enter' for them to take effect.

The amount of red, green, and blue light emitted is shown in the upper-left corner, and the "total color" -- the color you'd see with your own eyes -- is shown at the middle left.

This applet was written by Wolfgang Christian, Mike Lee, and Ansel Singer-Barnum at Davidson College.