Diamonds get their color either from a glow called fluorescence or trace elements contained within the stone.
Fluorescence: The Appearance of Color
Twenty-five to thirty-five percent of diamonds appear to glow a variety of colors including blue, yellow, orange, green, or a combination of these colors. This occurs when a carbon atom is missing from the lattice-like structure of carbon atoms that comprise a diamond. Often, these missing carbon atoms are replaced by nitrogen atoms, which when they come into contact with ultraviolet light, appear to glow a distinct color. The number of nitrogen atoms determines the color, for example, three nitrogen atoms will create a blue glow while one nitrogen atom will create a yellow glow.
Diamonds that are not clear or yellowish but an actual color are called fancy-color diamonds. In order for a diamond to be colored there must be additional trace elements and the distortion in the way that the stone formed. Fancy diamonds are yellow, brown, gray, orange, green, blue, white, black, purple, pink and red, which is extremely rare. In comparison to colorless diamonds only one colored diamond is found for every 10,000 making colored diamonds a sought after commodity. These diamonds are graded on the intensity of color rather than the lack of it as is the case with a colorless diamond.
“GIA Grading & Reports: Colored Diamonds, Gemstones & Pearls.” GIA: Guide to Understanding Diamond Quality and GIA Diamond Grading Reports. N.p., n.d. Web. 25 Oct. 2011. <http://gia4cs.gia.edu/cm/grading-reports/colored-diamonds.htm>.
“About Fluorescence.” Gemological Institute Of America. N.p., n.d. Web. 25 Oct. 2011. <http://www.gia.edu/lab-reports-services/diamonds/fluorescence.html>.