Gemstones' Color
Each colored stone species has its own beauty and value factors. The selection of colors in which a gemstone occurs is called its color range. Each gemstone has a different color range, and it can be broad or narrow. For example, most peridot is yellowish green, so it has a limited color range. Tourmaline on the other hand, comes in almost every color.
Within any gem’s color range some colors are more desirable than others. These top colors fall within limits that are generally accepted in the trade. A gem that features what the trade considers the most desirable color or colors is described as having fine color. For example, blue sapphire color range is from violetish blue to strongly greenish blue, only a small portion of that range is considered fine color. Sapphires of violet-blue to pure blue are generally considered the best, and are valued much more highly than greenish blue sapphires.
When light strikes the polished facets of a fashioned stone, some light is reflected, some is absorbed, and some is transmitted, this is called selective absorption. The transmitted wavelengths give the gem its basic color, called bodycolor. Bodycolor is a combination of hue, tone and saturation.
Hue is your first impression of a gem’s basic color. It might be described as red, green, yellow blue, purple ect. Some gems might require a combination of color terms. For example, a ruby might have some purplish face-up color, so you’d call it purplish red. Generally, gemstones that show only one color face-up are more valuable.
Tone is the darkness or lightness of a color. Many dark toned stones absorb so much light that they must be cut shallow to yield a lighter looking stone.
Saturation is a color’s strength or intensity. A large part of a gemstone's value lies in the saturation of its hue. Low saturation shows up differentially, depending on whether the hue is warm or cool. Generally, warm-colored stones with low saturation look brownish, while cool-colored stones with low saturation look grayish. Descriptions of low saturation levels include either brownish or grayish. High saturation is described as strong or vivid.
The GIA Colored Stones Grading System includes a description system that uses 31 hue names to describe colored gemstones.
GIA Color Description System
