Our radio explanation also includes two bits from an old Tin Pan Alley song by Yip Harburg (who wrote the lyrics for the Wizard of Oz score) and Vernon Duke, called "April in Paris" played by the Count Basie Band.

NPR: Not All Seasons Are Created Equal

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