Subtle color variations can have a significant impact on diamond value. The value of two diamonds with the same clarity, weight, and cut can differ solely due to color. Even the smallest amount of color can make a significant difference in value.
Diamonds come in a variety of colors. Colorless diamonds to light yellow and brown diamonds fall within the normal color range. Colorless diamonds are the most valuable within that range because they are the rarest. They established the benchmark for grading and pricing other diamonds in the normal color range.
When exposed to ultraviolet (UV) radiation, many diamonds emit a visible light known as fluorescence. UV radiation is all around us, even though it is invisible to the naked eye. It is contained by sunlight. It is also emitted by fluorescent lights. Fluorescence can be seen in approximately 35% of gem diamonds under the right conditions.
The most common fluorescent color in gem-quality diamonds is blue. Fluorescence can be white, yellow, orange, or a variety of other colors in rare cases.
In sunlight, strong blue fluorescence can make a light-yellow diamond appear colorless. Because blue and yellow are color opposites that tend to cancel each other out, blue fluorescence obscures the yellow color. If the fluorescence is too strong, the stone may appear cloudy or "oily," lowering the diamond's value.
DIAMOND COLOR EVALUATION
The absence of color is used to evaluate the color of most gem-quality diamonds. A chemically pure and structurally perfect diamond, like a drop of pure water, has no hue and thus a higher value. The GIA D-to-Z color-grading system compares a stone's colorlessness to masterstones of known color value under controlled lighting and viewing conditions.
The D-to-Z color-grading scale developed by GIA is the most widely used grading system in the industry. The scale starts with the letter D, which represents colorlessness, and progresses to the letter Z, which represents an increasing presence of color. Many of these color distinctions are so subtle that the untrained eye cannot see them; however, these distinctions make a significant difference in diamond price and quality.