How to draw GtkImage in runtime?

["George Brink" <siberianowl yahoo com>]

I need to draw several tool buttons with colored circles and rectangles on 
them.
I thought of doing something like:
----------
GtkToolItems *color_buttons[COUNT_OF_COLORS];
GtkWidgets *color_icons[COUNT_OF_COLORS];
GdkColors colors[COUNT_OF_COLORS] = {.....};
..... /// here is initialization of tool buttons
for( i = 0; i<COUNT_OF_COLORS; i++) {
       GdkPixbuf *icon = gdk_pixbuf_new(GDK_COLORSPACE_RGB, TRUE, 8, 40, 
40);
       GdkDrawable *dicon = ????
       //// how to get GdkDrawable from GdkPixbuf???
       GdkGC *gc = gdk_gc_new(dicon);
       gdk_gc_set_rgb_fg_color(gc, &(colors[i]));
       gdk_draw_rectangle(dicon, gc, TRUE, 2, 2, 36, 36);
       color_icons[i] = gtk_image_new_from_pixbuf(icon);
       g_object_unref(G_OBJECT(dicon));
       g_object_unref(G_OBJECT(icon));
       g_object_unref(G_OBJECT(gc));
       gtk_tool_button_set_icon_widget(GTK_TOOL_BUTTON(color_buttons[i]), 
color_icons[i]);
}
------------
And I am stuck on converting GdkPixbuf to GdkDrawable...

What is the easiest way to make a brand new GtkImage and draw something on 
it in runtime?