A good reason (which is why many companies use it) for 48 bits / pixel
is so you can use double buffering (for animating scenes) - i.e. you have
2 * 24-bit planes. You write to the one in the background, and then FLIP! 
-- the entire screen updates to the second image-plane. The screen updates 
in one refresh and you don't see different objects appearing in the order 
that they're drawn (as in the CAD/MacDraw effect). Now your ready to update 
the image that used to be in the foreground.

Steve. (thssstb@iitmax.iit.edu / iris.iit.edu)