From the Internet:
"Where did the term "white elephant" originate? As the story goes, it had something to do with the great showman, P.T. Barnum. Barnum, always looking for a new source of entertainment to bring in the crowds, was earnestly seeking a new attraction when his prize attraction, Jumbo the Elephant, was killed by a train.
Barnum needed a replacement and not just any replacement would do. Barnum decided that an albino elephant would do the trick and bring the masses back with their money. Barnum found a "white" elephant, but the problem was that most people who had paid good money to see the animal thought its color was closer to yellow than to white. Thus, the term "white elephant" represents something with a value exaggerated beyond its true worth. "