white LEDs not usually made with R G and B combined, but instead use just B and a color conversion sheet of phosphor.

http://nina.ecse.rpi.edu/shur/Tutorial/GaNtutorial3/sld009.htm

http://ledmuseum.home.att.net/

http://www.semiconductor.agilent.com/news/pr/15mar99.html

from the people who brought us the cool flashlamp pages:

http://www.misty.com/~don/led.html