Not meaning to be a fly in the ointment, or to sound like an ABC
detergent commercial, but "i can't tell the difference" between Rich's
test pix, even on the "millions of colors" setting (i usually use 256,
to save memory and allow things to run faster)- of course my monitor is
rather old, so perhaps it only makes a big difference on higher-quality
monitors.  That said, the colors are quite good (IMHO) on both of them,
so i would say if "millions of colors" is difficult for you, 256 will in
most cases be quite sufficient.
 
-Ross M.