In question 3.3, I said that certain widgets didn't have associated X windows, and for that reason were unable to handle events or be styled and coloured. These widgets are (add a Gtk in front if they look unfamiliar):

 Alignment
 AspectFrame
 Arrow
 Bin
 HBox
 VBox
 Frame
 Image
 Label
 Pixmap
 ScrolledWindow
 HSeparator
 VSeparator
 Table