One common point of confusion when consumers are shopping for yellow diamonds is the distinction between true fancy diamonds and white diamonds that have low grades for color, Clark said. The most colorless white diamonds are graded D and work their way down the alphabet as their nitrogen levels rise adding more yellow and brown to the diamonds. As the grade gets closer to Z, the diamond's value shrinks.

On the other side of Z, however, is when diamonds become fancy. The Gemological Institute of America rates these diamonds as faint, very light, light, fancy light, fancy, fancy dark, fancy intense, fancy deep and fancy vivid.

About the colors

Colored diamonds get their hues from various causes. Yellow diamonds have higher concentrations of nitrogen than white diamonds. Green diamonds get their shade from natural radiation. Blue diamonds contain traces of boron. The dark grayish-blue 45.52 carat Hope Diamond is one of the world's most famous, sought-after and costly diamonds.

Red and pink diamonds get their shades from defects in the crystal formation. Mariah Carey's engagement ring from Nick Cannon is a 17-carat square emerald-cut pink diamond, surrounded by 58 intense pink diamonds and two half-moon diamonds on each side. Estimated cost: $2.5 million.

Oklahoma women opting for colorful engagement rings are gravitating more toward blue sapphires, Gordon said, after Prince William gave Catherine, now Duchess of Cambridge, the sapphire-and-diamond engagement ring that had belonged to his mother, Princess Diana.

Black diamonds, which once were mainly used for industrial purposes, now are being used by jewelry designers to create stunning jewels. Another unusual diamond material is found in raw diamonds that are sliced and used in jewelry. These diamonds often have a brown hue. The thin slice allows a diamond to cover more surface area and look larger than its true size.