I rather agree that if one wanted to wear a tartan in honor of the Black Watch, most would simply choose the Black Watch tartan. However, I wish them luck.

For those that have commented that the Black Watch tartan looks good "with a bit of color added," there are a host of tartans that have been created by simply adding various colored stripes to the Black Watch.

Those that come immediately to mind:
Gordon
Forbes
Lamont
MacKenzie
Robertson Hunting
Farquarson
Scottish National

There are, of course, many others.