If that last bit seems like an exaggeration, the prices some famous diamonds have fetched at auction should convince you it is not.     The Pink Star A colored diamond is about as rare as a blue supermoon, which is why they cost so monumentally high. The Pink Star weighs 59.6 carats and is the biggest known diamond to have been graded Vivid Pink. Not surprisingly, it sold at $71 million. The Oppenheimer Blue Diamond The Oppenheimer Blue Diamond is the biggest diamond the world to carry a Vivid Blue grade. At 14.62 carats, it is also jewel coveted by the sort of people who already have everything they need in life, including a fortune that is hard to spend, and lots of costly diamond rings. Predicted to fetch somewhere around $40 million, it sold for more than $57 million at auction. The Orange Diamond A 14.82 carat stone that landed its own story in the acclaimed Forbes magazine, this diamond sold for $35.54 million, which is $2.4 million per carat.