Blue Diamonds
Blue Diamond Jewelry is a stunning form of "fancy colored diamonds" that is recently gaining in popularity among diamond and jewelry fans
Blue diamonds are natural, authentic white diamonds that have been heat and/or pressure treated to obtain their beautiful blue hue. So although blue diamond jewelry is treated, it is nevertheless a genuine diamond.
There are also naturally occurring blue diamonds, however, they are exceptionally rare. Blue diamond jewelry made by purely by nature, can cost as much as several hundred thousand dollars or more.
Treated blue diamonds, however, will cost significantly less and is a fashionable and unique alternative to a regular white diamond -- and they can cost less than white diamonds as well, at approximately half the price, for a quality colored diamond piece.
The reason blue diamond jewelry can cost less is because you do not need to start with a perfectly white diamond since you are going to be treating it anyway to change the color to blue. A fancy colored diamond producer, will start with a yellowish or low color grade diamond and treat it blue, therefore costing less than a high-end white diamond. Where the price differences come into play, however, are in the clarity and inclusion level of that diamond.
A popular form of colored diamonds, blue diamond rings , for example, will often be an I1 or I2 clarity diamond due to the fact that treating the diamond blue will mask most of the inclusions -- so a higher end diamond is often not needed, thereby reducing the cost of a colored fancy diamond in this way also. Some, however, will opt for an SI1-SI2 clarity blue diamond, which is more expensive, but often worth the upgrade, especially if purchasing the diamond for an engagement or wedding ring. Even so, the price will often still be less than a white diamond.
Source: http://www.articlebiz.com/article/159568-1-blue-diamond-jewelry/
Added: May 8, 2008