All objects above absolute zero radiate heat. The radiation is due to the random motion of charged particles in them. Greater the temperature, greater the random motion and greater the amount of radiation emitted. And this energy radiated has various wavelengths in it. The spread of energy amongst various wavelengths and the appearance of a black body at different temperatures are shown in the applet. The black body we are talking about is just an idealized hot body. As the temperature of the body emitting radiation increases the brighter part of the spectrum shifts towards shorter wave lengths. This can be observed in the spectrum choice - you need to change the temperature by adjusting the slider. This also is seen as the dominant wavelength in the graphs choice. Four graphs are shown for four different values of temperature. The peaks can be seen to shift towards the lower wavelength side for higher temperatures. Also the peaks for higher temperatures are higher indicating the increase in the total energy radiated. The overall appearance of the hot body, that is, the color of the body as it appears to the eye is shown in the color & temperature choice.