+in many of the following examples. Here we revert the color
+of the note head to the default value for the final two notes:
+
+@lilypond[quote,fragment,ragged-right,verbatim,relative=1]
+c d
+\override NoteHead #'color = #red
+e f g
+\override NoteHead #'color = #green
+a
+\revert NoteHead #'color
+b c
+@end lilypond
+
+@strong{\once prefix}
+
+Both the @code{\override} and the @code{\set} commands may be
+prefixed by @code{\once}. This causes the following
+@code{\override} or @code{\set} command to be effective only
+during the current musical moment before the property reverts
+back to its default value. Using the same example, we can
+change the color of a single note like this:
+
+@lilypond[quote,fragment,ragged-right,verbatim,relative=1]
+c d
+\once \override NoteHead #'color = #red
+e f g
+\once \override NoteHead #'color = #green
+a b c
+@end lilypond