[Groff] Groff Pic and colored objects!

[pod]

Hi all
Here is a short pic example
.PS
box height 0.3 "foofoo";
arrow arrowwid 1;
box width 3 height 3;
{"foofoo" at last box .n + (0,-0.1);}
box  width 1.8 height 1.5 at last box .w + (1.5,0);
.ps 8
{"\fBfoofoo()\fR" at last box .n + (0,-0.3);}
.PE

I just wanna know how I can make e.g. a box gray?
I know I can use e.g. box color "yellow" width 3 height 3;
but not e.g. box fill 0.5 width 3 height 3;

I use this command groff -p file | ps2pdf - file.pdf
How can I define own colors?


best regards pod