This will give your frame a background colour.
Normally, without this option, the frame will only be coloured for users on the Mac.
Where this option is used, a coloured frame will be produced on all platforms.
::tclmacbag::colorframe .f -background #828282
::tclmacbag::colorframe .g -background white
The colour #B2B2B2 is suggested as a good one to choose to mimic the general appearance of "metal" and "brushed metal" styles on the Mac.