I happened upon an amazing resource late last night.
It's called the Colored Diamond Encyclopedia and it is a wonderful resource about natural colored diamonds. The site is credited to Arthur Langerman of Antwerp, Belgium.
The Colored Diamond Encyclopedia site is well worth seeing, as its focus is natural colored diamonds. It covers topics such as history, geography, famous natural colored diamonds, the science of colored diamonds, the current market for colored diamonds, a pricing guide (very helpful per carat retail estimates), quality grading, etc.
The geography page is great for finding out, on a world map, where diamonds are mined. It also tells you what colors are found where and in what quantities. Very comprehensive and informative.
The quality grading page is a very good tool. Whereas colorless diamonds have the full scale of the four (or five, the fifth being Cost) Cs, the colored diamond quality scale is different. It essentially illuminates how color is more valuable than any of the other Cs when grading colored diamonds. A colored diamond is less like a diamond and more like a colored stone in this regard. Color is everything!
When you load the front page of the site, it scrolls through nearly thirty natural colored diamonds, telling what each one's color is. It is a complete and very thorough color charting and is really beautifully executed.
There are excellent photos of many famous natural colored diamonds, incuding the Pumpkin Diamond (at left), a 5.54 carat fancy vivid orange diamond, the largest and most valuable orange diamond in the world.
Its price? Well, if it was for sale, it would fetch about $3 million. It's the Great Pumpkin!
(photo from the Colored Diamond Encyclopedia)