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GIA COLORED GEMSTONE DESCRIPTIONS
Color Description for Colored Gemstones is categorized using 31 different color hues; along with gemstone color Saturation and Tone.
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Body Color plays a large role in rarity.
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Blue Sapphires are treasured for their deep beautiful lively predominately Blue color. Yet, they vary in color range from very slightly greenish Blue to violetish Blue. In this case, the body color of the stone is matched against the color chart.
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Tone and saturation are then graded.
 VioletGIA Colored Gemstone Color Palette |  violetish Purple |  Purple |  reddish Purple |  Red Purple; Purple Red |
|---|---|---|---|---|
 strongly purplish Red |  slightly purplish Red |  Red |  orangy Red |  Red Orange; Orange Red |
 reddish Orange |  Orange |  yellowish Orange |  orangy Yellow |  Yellow |
 greenish Yellow |  Yellow Green; Green Yellow |  strongly yellowish Green |  yellowish Green |  slightly yellowish Green |
 Green |  very slightly bluish Green |  bluish Green |  very strongly bluish Green |  Green Blue; Blue Green |
 very strongly greenish Blue |  greenish Blue |  very slightly greenish Blue |  Blue |  violetish Blue |
 bluish Violet |
TONE AND SATURATION
The highest prized colored gems contain the most color saturation, along with a medium to medium dark tone for vibrancy.
A gemstone's Tone defines where it stands on a contrasting light to dark scale.
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The typical tones used in grading, label a colored stone from:
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very light (2) to very dark (8) in tone
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A gemstone can be strong in color saturation, but if the Tone is very dark, then it can be difficult to see the color of the colored stone.
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A medium to medium dark Tone is best for viewing color in a gemstone.
Color Saturation is also very important to take into account.
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There are six classes to categorize color saturation in:​
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brownish (1) to vivid (6) saturation
Here is an example of warm color tones.
Here is an example of cool color tones.
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Notice cool colors have a grayish appearance due to the lack of color saturation. Just the same, stones warm in color appear brownish.
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When purchasing a gemstone, knowing these particulars can be very helpful.
In conclusion, a stone's Body Color plays the largest role in classifying a Gemstone's Variety.
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Tones that are too dark, or too light can be weak in color; stones that are too dark can prevent any color from being seen altogether.
In some cases, color Saturation can even determine a gemstone's variety. Gemstone Variety must be taken into account when grading for saturation.
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A (slightly purplish Red) Pink Tourmaline can have a moderately strong color saturation with a medium tone. Let us suppose the Pink Tourmaline were two color saturation grades higher with the same tone. That very same colored gemstone may become reclassified as a Rubellite (Red Tourmaline.)
EXPRESSION: Tone/Saturation + Body Color (color abbreviation seen on color wheel)
FOR EXAMPLE: A Gemologist could describe the color quality of an Aquamarine Gemstone by:
light, strong very strongly greenish BLUE (or) 3/5 vstgB: Tone, Saturation, Body Color
Below is a Ruby. See if you can now name the color according to GIA?
This is a LOWER EXTRA FINE Color Grade.
An UPPER EXTRA FINE Color Grade would be more like medium to medium dark in Tone, vivid in color Saturation, and Solid Red (5-6/6 R)
