Color zoning is a term used to describe gemstones with colors that are located only in some parts of the stone. Zoning is considered undesirable. However, some zoning is more severe than other types of zoning. The chart below outlines the four different types of color zoning.
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.
In stones without color zoning, the color is evenly distributed across the stone.
Gradual zoning refers to a blended weakening of the color.
Visible color zoning refers to stones that have only patches or layers of color. Colors may change abruptly in such stones.