Or you could simply write text in white letters on a black background
to begin with... :-))

Sometimes your print-out is more grey than black, which is because of a
toner-saving option that often is enabled by default. Most laser
printers do this to avoid printing large areas of pure black. You can
either disable toner saving in the advanced printing options dialogue
or you just chose a very very VERY dark red (or blue or whatever) as a
backgrund - which the printer will print as black anyway, without
bothering with saving toner...

/K