\version "2.19.47"

funcA =
#(define-music-function (mus)(ly:music?)
   #{
     #mus
   #})

funcB =
#(define-music-function (mus)(ly:music?)
   #{
     \once \override NoteHead.color = #red
     #mus
   #})

funcC =
#(define-music-function (mus)(ly:music?)
   #{
     \once \override NoteHead.color = #blue
     \parenthesize #mus
   #})

{
  % funcA: point-and-click points tofunction invocation
  \funcA c'
  % funcB: point-and-click points to music
  \funcB d'
  % funcC: point-and-click *also* points to function invocation
  \funcC e'
}