London's Natural History Museum this month begins what it calls a "blockbuster exhibition" of some of the world's most spectacular white and colored diamonds. Among the stones being featured: The 203.04 ct. D Flawless De Beers Millennium Star, the world's largest flawless stone. Cut from a rough diamond of 777 cts., it was unveiled in 1999 at the Millennium Dome in London where it became the target of a foiled robbery attempt. This is the first time it has been on public display in the United Kingdom since then; The Incomparable: the 407.48 ct. yellow that is the third-largest diamond ever cut; The Steinmetz Pink: This 59.60 ct. oval is the world's largest flawless fancy vivid pink stone. It was worn by model Helena Christensen in May 2003; The Ocean Dream: the world's largest naturally occurring fancy deep–blue green diam