In order to keep your black clothes black, use a dark or colour clothing 
laundry detergent such as Dreft Dark.  Avoid washing liquids that 
contain bleach or whiteners.

Do not put too much detergent into a wash -- one capful will normally be 
enough -- and never wash at more than 40C.  Sunlight is also a powerful 
bleaching agent, so dry clothing indoors if possible.

If you find tiny white specks appearing on your clothing when you enter 
a club, it is caused by the ultraviolet lighting.  The best way to get 
rid of these filaments is with a product such as Sticki-Mitts.

If you're interested in redyeing your black clothes, see the Dye It 
Black FAQ <http://www.darkwave.org.uk/~bob/dye.faq.html>.