Answering my own question, inserting this line solved the problem:
> { gsave
> [ /ca .5 /SetTransparencypdfmark
.5 .setopacityalpha true .settextknockoutWalt -~
Answering my own question, inserting this line solved the problem:
> { gsave
> [ /ca .5 /SetTransparencypdfmark
.5 .setopacityalpha true .settextknockoutWalt -~