It remained for the 1939 MGM version to add the image of the rainbow to the iconography (courtesy of lyricist Yip Harburg), to make the whole story a Technicolor dream and, most significantly, to saturate the entire narrative in one of the most glorious scores (by Harburg and composer Harold Arlen) of any film or show.
WSJ: The Road Well-Traveled: Oz the Great and Powerful