The 1939 movie "The Wizard of Oz" contained a horse that changed color, what material did they use to achieve this effect?

In the 1939 movie "The Wizard of Oz," the horse that changed color was achieved through the use of gelatin. Gelatin is known for its ability to absorb and reflect light, making it ideal for creating visual effects in films. By applying gelatin to the horse's coat, the filmmakers were able to alter its appearance and create the illusion of it changing colors, adding a touch of magical realism to the movie.