mash returns the following for 'winfo visualsavailable .':
{truecolor 15} {truecolor 15} {truecolor 15} {truecolor 15} {truecolor 15} {truecolor 15} {truecolor 15} {truecolor 15} {truecolor 15} {truecolor 15} {truecolor 15} {truecolor 15} {truecolor 15} {truecolor 15} {truecolor 15} {truecolor 15} {truecolor 15} {truecolor 15} {truecolor 15} {truecolor 15} {truecolor 15} {truecolor 15} {truecolor 15} {truecolor 15} {truecolor 15} {truecolor 15} {truecolor 15} {truecolor 15} {truecolor 15} {truecolor 15} {truecolor 15} {truecolor 15}
wish returns the following:
{truecolor 24}
X11 0.1 (XFree86 4.2.1)
2003: Apple Computer, Inc. + XFree86 Project, Inc.
Logged In: YES
user_id=238724
Modified ui-visualframe.tcl to use TrueColor/16 if {truecolor 15} is returned. My monitor was set at Thousands of colors at the time, although {truecolor 15} is returned even when set at Millions of colors.