Написать пример клиентского окна на X11 или GTK под графический стол Gnome.

#include <gtk/gtk.h>

static GtkWidget *window = NULL;
static GtkWidget *da;
static GdkRGBA color;
static GtkWidget *frame;
static gboolean
draw_callback (GtkWidget *widget,
cairo_t *cr,
gpointer data)
{
gdk_cairo_set_source_rgba (cr, &color);
cairo_paint (cr);
return TRUE;
}

static void
response_cb (GtkDialog *dialog,
gint response_id, gpointer user_data)
{
if (response_id == GTK_RESPONSE_OK)
gtk_color_chooser_get_rgba (GTK_COLOR_CHOOSER (dialog), &color);
gtk_widget_destroy (GTK_WIDGET (dialog));
}
static void
change_color_callback (GtkWidget *button, gpointer data)
{
GtkWidget *dialog;
dialog = gtk_color_chooser_dialog_new ("Changing color", GTK_WINDOW (window));
gtk_window_set_modal (GTK_WINDOW (dialog), TRUE);
gtk_color_chooser_set_rgba (GTK_COLOR_CHOOSER (dialog), &color);
g_signal_connect (dialog, "response", G_CALLBACK (response_cb), NULL);
gtk_widget_show_all (dialog);
}

GtkWidget *
do_colorsel (GtkWidget *do_widget)
{
GtkWidget *vbox;
GtkWidget *button;

if (!window)
{
color.red = 0;
color.blue = 1;
color.green = 0;
color.alpha = 1;
window = gtk_window_new (GTK_WINDOW_TOPLEVEL);
gtk_window_set_screen (GTK_WINDOW (windowgtk_widget_get_screen(do_widget));
gtk_window_set_title (GTK_WINDOW (window), "Color Chooser");
g_signal_connect (window, "destroy", G_CALLBAC (gtk_widget_destroyed),&window);
gtk_container_set_border_width (GTK_CONTAINER (window), 8);
vbox = gtk_box_new (GTK_ORIENTATION_VERTICAL, 8);
gtk_container_set_border_width (GTK_CONTAINER (vbox), 8);
gtk_container_add (GTK_CONTAINER (window), vbox);
frame = gtk_frame_new (NULL);
gtk_frame_set_shadow_type (GTK_FRAME (frame), GTK_SHADOW_IN);
gtk_box_pack_start (GTK_BOX (vbox), frame, TRUE, TRUE, 0);
da = gtk_drawing_area_new ();
g_signal_connect (da, "draw", G_CALLBACK (draw_callback), NULL);
gtk_widget_set_size_request (da, 200, 200);
gtk_container_add (GTK_CONTAINER (frame), da);
button = gtk_button_new_with_mnemonic ("_Change the above color");
gtk_widget_set_halign (button, GTK_ALIGN_END);
gtk_widget_set_valign (button, GTK_ALIGN_CENTER);
gtk_box_pack_start (GTK_BOX (vbox), button, FALSE, FALSE, 0);
g_signal_connect (button, "clicked", G_CALLBACK (change_color_callback), NULL);
}

if (!gtk_widget_get_visible (window))
gtk_widget_show_all (window);
else gtk_widget_destroy (window);

return window;
}