In "The Way You Look Tonight", Ginger Rogers is seen to be washing her hair. The crew tried various soaps, shampoos, and even egg white, but it always ran down her face too quickly. They achieved success with whipped cream.
Fred Astaire always insisted that his dance routines be filmed in one continuous camera shot, showing the dancer(s) from head to foot. However, in the "Never Gonna Dance" number, there is an obvious moment when Astaire and Rogers reach the tops of their respective winding staircases that the camera shot changes quickly to reflect the fact that the filming camera had to be brought upstairs to shoot the close-up finale of the dance number.
The film originally began with a musical number, "It's Not in the Cards," which was cut due the film's length and because the number was judged as not very good. Only a bit remains in the final version. The music is also used in the background during the first few scenes.
The original concept of "Bojangles of Harlem" was actually much more elaborate than what ended up on film. A scenario called "Hot Fields" was prepared as a loose parody of the all-black vehicle "Green Pastures." It would have involved the Bojangles character traveling through a variety of stylized sets representing Heaven, Hell and jungle locations, and would have involved many routines with that most familiar Bill Robinson setting - stairs. Thirty-three scenes would have been required. No doubt such an elaborate series of sequences was deemed to be too expensive to construct and film. All that remains in the film is an introduction to the character involving an outsized bowler hat which turns into enormously long legs.
During rehearsals for the "Bojangles of Harlem" sequence, Hermes Pan noticed that three light sources were creating a group of Fred Astaire shadows dancing in perfect sync, and got the idea for the special effects shots in the dance. Astaire was filmed in silhouette, then tripled. The dance proper was then filmed against a process screen and combined with the shadow footage optically by RKO effects chief Vernon Walker. The effect was by no means perfect, however, as there is some "bleeding" of the image - the process screen shows through Astaire's hair at several points.