A gemstone’s grade, and thus value, is determined in large part by the stone’s color. When considering a gem’s color, buyers should keep in mind that there are three primary colors: blue, yellow, and red. All other colors are a combination of these primary colors. This means that most stones in secondary or tertiary colors will have strong, primary hues. This is why green stones are often described as yellow-green or blue-green. Many gemstones also include elements of white, gray, and black. In the traditional color system, these are considered neutral colors. When neutral colors are present in a stone, the stone must be evaluated in terms of saturation, hue, and tint. The chart below provides definition for these terms and for the color grading terms with which they are associated.
Saturation refers to the ratio of grays and other colors in a given stone. The higher the saturation, the less gray a stone contains. In general, stones with a very high saturation are much more valuable than stones with a high percentage of gray.
The word “hue” is often used in place of the word “color.” The hue of an emerald, for instance, is green. Gray, white, and black are not hues, meaning that they are not considered true colors. Some hues of gems are much more valuable than others. Such values tend to fluctuate over time and depend largely on the preferences of jewelers and buyers during a given era.
Any color mixed with white is described as a tint. In the majority of gemstones, the higher the tint, the less valuable the stone. Gems are considered more valuable when they are free of white. However, a handful of gems are considered more valuable when they are tinted.
The color grade of a stone describes the strength of the primary color. A stone that is 100 percent yellow would contain absolutely no other colors. Stones are generally assigned a higher overall grade if they have very pure coloring.
Color tone describes the amount of black or white mixed into a stone. This term is used to describe whether the stone is very light or very dark.
A gemstone is graded according to both color grade and color tone. Buyers who wish to buy the more valuable semi-precious gemstones should conduct independent research to determine ideal color grade and color tone values. Remember that it is not necessary to buy gems that are graded highly. Personal preference should almost always take precedence when buying semi-precious gemstones.