Out of curiosity, I did some research to see if there were real white elephants. Here's what I found:
The king would punish a servent by giving him a white elephant. As this type of elephant needed special care, it was a serious commitment to take care of it. This elephant was not a means for working any laborius tasks, and was not good for much of anything except to see to its care. That's where the quote "white elephant" sale originated from. It seems to be based on fact, and not a myth, and thought it was an interesting story.
There are white elephants, but rare, from what I understand.