[Groff] string variable in pic

[Heinz-Jürgen Oertel]

Hello,
I'm searching for a way to put strings in pic variable, but found no way 
doing it.
What I like to do  is something like:

.PS
bcolor = "red"

define cbox {
    box wid $1 color bcolor
}
.PE

.PS
cbox(1) "this is red"
bcolor "yellow"
cbox(1) "this is yellow"
.PE

Another interesting feature would be if 
\n[.M] could return the numerical values of the color components.
In this case one could define a new color which is sometimes darker or more 
bright, or "more red" etc. This can be used to produce shaded colored boxes 
in pic.

Hope I get help
 Regards
  Heinz