I tested this on a black-on-transparent EPS that was created via MetaPost,
and it seems to work fine.  If you are not using Linux (or Unix or Mac OS
X), let me know and I can probably put together a quick HTML page to do
this on my server.

> cat foo.eps | sed -e "s/0 0 0 setrgbcolor/1 1 1 setrgbcolor/g" > bar.eps

It simply translates the (0,0,0) triplet (which is black) to the (1,1,1)
triplet (which is white).  This is very simplistic and may not do all that
you want.

Troy Henderson