[Last modified: May 95]

Answer: Ken Lee wrote: There is no direct API for setting this, but you can
set it through resource files with "*XmScale*troughColor: red".

Ken Sall, ksall@cen.com, adds: If you need to do this at runtime, you can use
XtGetValues to get the scale's children, find the scrollbar, and set the
XmNtroughColor:

#include <Xm/ScrollBar.h>  // for XmIsScrollBar

Pixel selectColor; // assume this is set to the desired color
WidgetList *kids;
int nkids;
Arg argList[1], tmpargs[2];
int i, s, t ;

i = 0;
XtSetArg ( argList[i], XmNtroughColor, selectColor ); i++;

// Unfortunately, scale does not have a direct way
// to get its scrollbar widget, so use Composite resources
s = 0;
XtSetArg (tmpargs[s], XmNnumChildren, &nkids ); s++ ;
XtSetArg (tmpargs[s], XmNchildren, &kids ); s++ ;
XtGetValues ( widgetId, tmpargs, s );
for ( t = 0; t < nkids; t++ )
    {
    if ( XmIsScrollBar ( (Widget) kids[t]) ) // from ScrollBar.h
        {
        XtSetValues ( (Widget) kids[t], argList, i );
        }
    }