[R-gui] Tktable on Mac OSX with X11, systemWindowBody color

Hi,

I'm doing some testing of my R/TclTk application on Mac OSX with 
Apple X11 (based on Xfree86), (with Tcl/Tk installed via the 
Apple Developer Tools) and I've come across a problem 
when trying to use the table widget in Tktable:

This works fine in wish (the Tcl/Tk interpreter) :
% package require Tktable
% toplevel .tt
% table .tt.table1
% pack .tt.table1

But when I try it in R (even when using the low-level .Tcl(...) 
interface which should be similar to wish:

library(tcltk)
addTclPath("/Library/Tcl")
.Tcl("package require Tktable")
.Tcl("toplevel .tt")
.Tcl("table .tt.table1")

Error ...
    [tcl] unknown color name "systemWindowBody".

"grep systemWindowBody *" in the Tktable package directory 
revealed just one reference to it, in the binary file, 
libTktable2.8.dylib
I don't have the Tcl/Tk source handy and I couldn't find 
systemWindowBody in the R source or in the tcltk 
R package source.

Has anyone come across this problem before?

Searching the web, I found some of the Mac Tk source:
http://www.openmash.org/lxr/source/mac/tkMacDefault.h
which has:
#define NORMAL_BG       "systemWindowBody"
and the "NORMAL_BG" page says 
"Defined as a preprocessor macro".
which didn't help me much.  

I even tried things like:
  .Tcl("set systemWindowBody gray")
   Sys.putenv("systemWindowBody","gray")
with no success.

Regards,
James