https://invisible-island.net/xterm/xtoolkit/
XtSetWMColormapWindows - Set the value of the WM_COLORMAP_WINDOWS prop-
erty
#include <X11/Intrinsic.h>
void XtSetWMColormapWindows(Widget widget, Widget* list, Cardinal
count);
widget Specifies the widget on whose window the WM_COLORMAP_WINDOWS
property will be stored. Must be of class Core or any sub-
class thereof.
list Specifies a list of widgets whose windows are are potentially
to be listed in the WM_COLORMAP_WINDOWS property.
count Specifies the number of widgets in list.
XtSetWMColormapWindows returns immediately if widget is not realized or
if count is zero. Otherwise, XtSetWMColormapWindows constructs an
ordered list of windows by examining each widget in list in turn and
ignoring the widget if it is not realized, or adding the widget's win-
dow to the window list if the widget is realized and its colormap
resource is different from the colormap resources of all widgets whose
windows are already on the window list.
Finally, XtSetWMColormapWindows stores the resulting window list in the
WM_COLORMAP_WINDOWS property on the specified widget's window.
X Toolkit Intrinsics – C Language Interface
Xlib - C Language X Interface
X Version 11 libXt 1.1.5.2 XtSetWMColormapWindows(3)