Answering my own question, inserting this line solved the problem:
> { gsave
> [ /ca .5 /SetTransparencypdfmark
.5 .setopacityalpha true .settextknockout
Walt
-~
Answering my own question:
http://pages.cs.wisc.edu/~ghost/doc/AFPL/6.50/Language.htm#Transparency
For some reason this was a bit difficult to find.
I just needed to adjust the code:
{ gsave
[ /ca .5 /SetTransparency pdfmark
.5 .setopacityalpha true .settextknockout
...
I have a PS file that contains something like this:
<< /AllowTransparency true >>
setdistillerparams
<<
/BeginPage
{ gsave
[ /ca .5 /SetTransparency pdfmark
/Helvetica-Bold findfont 42 scalefont setfont
.8 .85 .9 setrgbcolor 90 100 moveto 57 rotate
(Some Watermark
