The most desirable emerald colors are bluish green to pure green, with vivid color saturation and tone that’s not too dark. The most-prized emeralds are highly transparent. Their color is evenly distributed, with no eye-visible color zoning. If the hue is too yellowish or too bluish, the stone is not emerald, but a different variety of beryl, and its value drops accordingly.
The intensity of the green in the finest emeralds might not be equaled by anything else in nature.
Chromium, vanadium, and iron are the trace elements that cause emerald’s color. The presence or absence of each and their relative amounts determine the exact color of an emerald crystal.
Emerald appearance is sometimes associated with its mine location. Colombian emeralds are said to have a warmer and more intense pure green color. Zambian emeralds are said to have a cooler, more bluish green color. In spite of these theories, the truth is that emerald appearance overlaps between sources.