Why does the film "The Phantom of the Opera" start in black and white?

Beginning the movie with a black and white picture is an aesthetic ploy to create a feeling of nostalgia in spite of the beginning of the movie being only the end of the story. Some years have elapsed between the time of the phantom of the opera and its ensuing auction. For a first time audience, they will be curious to know the events which have led up to this auction. In a sense, viewers are given a cue when the actual story begins; that is, when the picture fades from its grayscale to full color. Such a drastic change in picture also induces a sort of excitement in the audience and helps to depict the opera as a lively, energetic, and colorful venue. When the picture once more returns to black and white, viewers, too, feel a sort of nostalgia and sadness for the events that occurred and the sad demise of the opera house.