Two weeks' worth of footage was shot with the characters having these looks until the film's director, Richard Thrope, was let go from the film, after MGM executives thought that the scenes he shot "did not have the right air of fantasy about them." The movie was paused and Dorothy and the Wicked Witch of the West's costumes were redesigned to what we saw in the final film:
Come to think of it...maybe its sophistication and useful knowledge is why no one else commented on this after being posted a full day ago...there's nobody to insult here.