The grading system for diamond color ranges D – Z, with D being colorless and Z representing a light yellow. However diamonds actually come in a range of colors including pink, blue and yellow. Everything beyond the Z rating is considered an ‘exotic’ or ‘fancy’ color. Excluding exotics, the more colorless the stone, the better is said to be the quality and therefore the higher is the price. While you can find many attractive diamonds in off-white and pale canary shades, their quality is purportedly somewhat less and their price decreases because of this. Ironically, once the diamonds veer from off white into stronger color variations, the price of the stone goes back up! With the ‘fancy’ colors, especially intense natural colors, you’ll look at greater expense due to the rarity of the stone.

Blue Diamond: These rings will be in the upper price bracket due to rarity, but they’re ideal when your focus is originality and uniqueness. A “natural blue diamond” is extremely rare and thereby costly; you’re well advised to proceed with caution before purchasing a ring advertised as “natural blue”.

Natural blue diamonds have undergone irradiation, which lends them their unique color. A general rule of thumb is that the darker the blue, the higher the quality.

An interesting piece of engagement-ring trivia: the Hope Diamond, probably our culture’s most famous diamond (which is on display in the Smithsonian Natural History Museum) is a blue diamond in antique cushion cut.

Yellow Diamond: As with other colored diamonds, rarity is more of a factor with the yellow or “canary” diamond, so expense will be greater. Intense yellow diamonds are of higher quality than pale yellow diamonds. Celebrities such as Jennifer Lopez, Brittany Murphy, and Carrie Underwood have been given stunning yellow diamond engagement rings, while Eddie Murphy and Charlie Sheen also opted for canary diamond engagment rings when proposing to their fiances.

Yellow is one of the more popular exotic colors currently, but there are many others available which are enticing to those on the look-out for something unique.

About.com has a great interview with experts from AMGAD Natural Color Diamonds. One important thing pointed out in this article is the grading scale used for colored diamonds. As opposed to running D – Z like the scale for regular diamonds, the fancy scale runs 1 – 9, with 1 meaning ‘Faint’ and 9 meaning ‘Fancy Vivid’. The more intense the color, the closer toward 9 you diamond is. Diamonds nearer 9 are considered the higher quality diamonds, and will therefore be more pricey.

Think carefully before investing in a colored diamond engagement ring. They are not every bride's cup of tea!

Our final installment on engagement ring styles will center on qualities not covered by cut and color, qualities such as number of diamonds used in the setting and whether to consider that famous designer-imposter diamond, the cubic zirconia.