Both white and black contains the entire light spectrum for color therapy.  White strengthens, cleanses, and purifies the entire energy system.  It can awaken our creativity.  It is a color that amplifies the effects of other colors.  Black is protective, grounding, and calms extremely sensitive individuals.  Black is most effective when used in conjunction with white which balances our polarities putting life and its craziness into proper perspective.  Black is always better used in combination with another color because often too much black can aggravate emotional and mental conditions.  I recommend How to Heal With Color, by Ted Andrews, to learn more about color therapy.