GENEVA: The largest internally flawless fancy vivid blue diamond ever put up for auction could sell for up to $50 million at a Christie's sale of rare jewels in Geneva on Nov 7, the auctioneer said on Thursday. Known as "Bleu Royal," this vivid blue diamond - which is set in a ring - is among the rarest ever to be unearthed. "What makes Bleu Royal so rare and special is its size.At 17.6 carats, it's the largest of its kind," said Rahul Kadakia, Christie's international head of...