When does yellow become orange, and orange become red? The question may sound a bit philosophical until you tie it to colored diamonds, where slight variations in color can mean huge differences in price.

Jewelry connoisseurs have gone crazy for colored diamonds. And their appetites were practically insatiable in 2013.

Going once. Going twice. Going three times. Sold for $83.2 million.

That was the winning bid for the 59.6 carat Fancy Vivid Pink Dream in November 2013 – the most ever paid for a diamond. The amount was comparable to prices paid for paintings by some of the masters.

As the creator of the 4Cs and International Diamond Grading System, GIA also established color grading standards and terminology specifically for colored diamonds, based on the color’s hue, tone, and saturation. Today, we identify some of the defining characteristics that help make fancy-color diamonds a true feast for the eyes.

Many people know that diamonds typically come in a range of colors from D to Z on the GIA color-grading scale.  However, most people don’t know how the naked eye sees color in a diamond.

Do you know how diamond color is evaluated? GIA kicks off its 4Cs Q&A series with color grading.