Diamond Color Undertones
By Victor Canera, GIA Graduate Gemologist · Updated
Many consumers today are unaware of the impact that a “color undertone” has on the appearance and ultimately the value of a loose diamond. The common misconception is that with progressively lower colors, diamonds move in a straight line from white through an increasing pure yellow. In reality, there are many color undertones other than yellow which can lead to drastically different appearing diamonds even within the same color grade.
Color Undertones Defined
Color undertones can be explained in layman's terms by thinking of them as being the hue and the combination of saturation and tone from the color spectrum. If the grade D represents the absence of any color in a diamond and Z is the most colored, the saturation of color increases progressively as you go down the color scale. Within these progressively higher color saturations in lower colors, you can have different hues of color. The most common and expected undertone hue in diamonds is yellow which is never noted in a lab report. Other hues or undertones besides yellow can also be found, the second most common of which is brown. Although more rare, greenish and grayish undertones also exist (Ref. 1-1). A gray undertone can be more clearly thought of as a tonal characteristic rather than saturation which slightly darkens the appearance of a diamond. A greenish undertone usually denotes diamonds sourced from the African country of Zimbabwe which are known for having this characteristic. In the "trade", the terminology “No BGM” (No Brown, Green or Milky) has become a commonly used term by traders to confirm that a diamond is not Brownish, Greenish or has a Milky luster. The first two terms of Brownish and Greenish are used to denote the color undertone while the term "milky" is used to define diamonds that have a slightly dull appearance without the superb luster and translucency that diamonds are known for. Milky diamonds are typically found with stones that have high levels of fluorescence. Traditionally, diamonds having an undertone other than yellow are considered undesirable by jewelers and are typically traded at a discount.
Frequently asked questions
What is a diamond color undertone?
A color undertone is the hue a diamond's body color leans toward beyond simple yellow — it can be yellow, brown, gray or green. Two diamonds with the same color grade can look quite different depending on their undertone.
Are diamond color undertones noted on the GIA report?
Yellow, the most common undertone, is not noted. The other undertones — brown and gray — are noted starting from the color K and lower on the report and can affect both appearance and value.
Do undertones affect a diamond's value?
Yes. Within the same color grade, a less desirable undertone such as gray or brown can lower value, while a clean, expected warm tone may be preferred.
