White diamonds is actually colorless diamonds. You often hear word white diamonds , yellow diamonds , chocolate diamonds and a few rare color such as blue and pink diamonds the compositorial that form this diamonds that is what give the diamonds color. White Diamonds or Colorless is formed when nothing else or minor trace of other elements mix with it.
In general, diamonds color rate from D to Z except for a few rare one that goes off the general rating. Click Here for GIA explain above diamonds color