Which colored diamonds are the most expensive per carat?
Red diamonds are by far the most expensive. Although your local jeweler might claim to sell red diamonds, there are actually only a handful of natural reds ever found and they can sell for hundred's of thousands of dollars per carat.
Green diamonds come next. The most famous green diamond is a 41 carat fancy green diamond that is set in a hat ornament made in 1768.
Other top colors (in order of price per carat) are:
Of course, there are other factors that apply to specific diamonds, such as clarity, size, the intensity of the color etc. that can distort this order. But this is generally the ranking of diamonds by color.
However, what about orange and purple diamonds? Let me know where you think they fit in the order or if you disagree with the order listed above.