"The speed at which the musical travels is Gower Champion. Otherwise, ... we’d still be waiting for scenes to change..." --- author John Anthony Gilvey in an interview with Harold Channer
The "brown-out," as Champion would sometimes call it, is the name for changing a scene in full view of the audience. Instead of stage lights being turned off completely during an act break - a black out - the lights might be dimmed and changing scenery and props would become a part of the choreography.
Gilvey is the author of the well-researched, detailed, and Marge Champion-endorsed biography Before the Parade Passes By: Gower Champion and the Great American Musical.
Watch the Gilvey interview on Gower Champion here. You can skip to the quote here; it is at 44:48.