If you are looking for blue diamonds, you will have to decide which type you are going to get: natural or man-made. Natural blue diamonds are extremely rare and therefore extremely expensive. The blue color in the diamond is caused by chemical impurities, usually, boron, or hydrogen. The diamonds range in color from a very light blue tint, to a deep royal blue. This is due to varying amounts of the chemicals in the diamond.
The deeper colored diamonds are worth the most money. Most people would rather have a consistent, deep hue, than a uneven, multicolored blue diamond.