yellow tinged diamonds are considered unattractive, such hues as pink or blue are thought to make a diamond more attractive. The Hope Diamond is probably the most well known blue colored diamond. Of all colored diamonds, red diamonds are the rarest type of all.

Colored diamonds occur in a rather restricted range of color. These include: white, steel grey, yellow, orange, blue, red, green, purple, pink and even brown and black. The coloration is caused by structural defects and interstitial impurities. Light is refracted differently through these flaws and results in different colored diamonds.

The gemological Institute of America uses a ‘D’ to ‘Z’ scale for grading the color ‘white’ diamonds, where ‘Z’ is yellow and ‘D’ is colorless. The color grade scale is as follows:

• colorless: D, E, F
• near colorless: G, H, I, J
• faint yellow or brown: K, L, M
• very light yellow or brown: N, O, P, Q, R
• light yellow or brown: S, T, U, V, W, X, Y, Z

Many other international diamond grading organizations have also decided to use the Gemological Institute of America’s color scale for grading diamonds.

So when do diamonds qualify as colored diamonds, per se? When a diamond is being graded and the color grade is beyond a ‘Z’ rating it is considered to be a colored diamond. These colored diamonds are then graded by a different set of guidelines similar to those used for colored gemstones, such as emeralds, rubies and sapphires.

For the most part, colored diamonds are graded the same as colorless diamonds with regard to clarity and other features. Interestingly, some diamonds have enough color to be graded low as a diamond but very high as a general colored gemstone.