-Finally we could make the bar lines invisible by coloring
-them white. The @code{grob-interface} specifies that the
+Finally let us try making the bar lines invisible by coloring
+them white. (There is a difficulty with this in that the
+white bar line may or may not blank out the staff lines where
+they cross. You may see in some of the examples below that this
+happens unpredictably. The details of why this is so and how to
+control it are covered in @ruser{Painting objects white}. But at
+the moment we are learning about color, so please just accept this
+limitation for now.)
+
+The @code{grob-interface} specifies that the