Sue,

Blast or some other real scientist may need to correct the specifics, but basically it has to do with the wavelengths of radiation (such as light or heat) reflected or absorbed. For example, if something appears blue, it's actually absorbing other colors of the spectrum but reflecting blue. White is reflecting all colors approximately equally. Black is absorbing all colors (wavelengths).

Since black absorbs all wavelengths, it also radiates in all wavelengths and therefore tends to radiate heat away more quickly. Try this: go out on a hot sunny day in a black coat. Then try a white coat. Most people will experience the black coat as significantly warmer because it will absorb heat from the sun whereas the white coat will reflect it.

Another experiment is to put two objects of equal temperature, one black, one white, into a refrigerator and chart the decline in temperature. All else being equal, the black one should cool slightly faster.

HJ