[gtkmm-documentation] Add a TODO comment

[Murray Cumming <murrayc src gnome org>]

commit cf399e4991799477826dc10263bd20e23f022075
Author: Murray Cumming <murrayc murrayc com>
Date:   Fri Jan 6 00:41:24 2012 +0100

    Add a TODO comment

 examples/others/window/wheelbarrow.cc |    2 ++
 1 files changed, 2 insertions(+), 0 deletions(-)
---
diff --git a/examples/others/window/wheelbarrow.cc b/examples/others/window/wheelbarrow.cc
index 3d4d5a1..8c063ba 100644
--- a/examples/others/window/wheelbarrow.cc
+++ b/examples/others/window/wheelbarrow.cc
@@ -151,6 +151,8 @@ Wheelbarrow::Wheelbarrow()
 
   realize(); // the widget must be realized to create the GDK window
   const Glib::RefPtr<const Gdk::Window> window = get_window();
+
+  //TODO: Use get_style_context() and Gdk::RGBA instead?
   const Gdk::Color transparent = Gtk::Widget::get_default_style()->get_bg(Gtk::STATE_NORMAL);
 
   const Glib::RefPtr<Gdk::Pixbuf> pixbuf =