How to Evaluate Diamond Color

A Detailed Guide on How to Evaluate a Color of a Diamond

Diamonds being one of the most precious gemstones are graded based on 4 Cs namely color, carat, clarity, and cut. Although, the color can vary from colorless to pink or brown, colorless is the most desirable and highly rated parameter.
Diamond, a transparent crystal made up of tetrahedral bonding between carbon atoms is the hardest natural substance present on the earth. The name originates from ancient Greek script- adamas. Although these gemstones have many uses, their most noticeable use is for adornment. Their exceptional physical feature of high dispersion index make them one of the most valuable gemstone. Dispersion of white light into array of spectral colors is their premier gemological feature.

The four major parameters, also known as the 4 Cs, carry the paramount importance while evaluating the quality and price. This 4 Cs are Color, Carat, Clarity, and Cut. So, it is of utmost importance to understand the grading and phenomena associated with it, if you are planning to purchase it. By understanding these parameters, you can decide which graded diamond to go for.

Although, a structurally perfect and chemically pure diamond can be defined as the one with complete transparent appearance with no hue or color, in reality no such gem size diamond can be found. The lack of color contributes towards higher grading. Hue is one of the main attribute of perceived color, besides lightness and chroma. The color is generally affected by few structural defects in its crystal lattice. Chemical impurities also contribute towards deviation of color from perfect white.

Hue and saturation of color decide its value. When more or less yellow hue is present, it is regarded as less expensive, while pink or blue hue can boost its price. One of its best examples lies in Hope Diamond which is dramatically precious. In general, the ones used in gemology are basically transparent with a little tint. They are also known as white diamonds. Nitrogen is the most common impurity found. Due to its presence in the structural bonding, replacing carbon atoms leads to yellowish, brownish tint.

Color Gradation

Although the gradation process exists from ancient ages, 20th century has seen more standardization based on the colors that are accepted worldwide. Mainly three organizations are responsible for this standardization of gradation system.

1. Gemological Institute of America (GIA) - The first laboratory to address the aspects of grading and holds high regard for its consistent and strict norms.
2. American Gem Society (AGS) - Although a new platform for gradation in comparison with GIA, it is renowned for a grading system based on numbers.
3. Diamond High Council (HRD) - Based in Antwerp, it is the authority to issue official certification.

20th century has seen emergence of a color gradation system ranging from D to Z, where D denotes for colorless and Z denotes for bright yellow coloration. This system has universal appeal unlike other systems present earlier. It assesses the diamond in comparison with the benchmark set in the presence of standardized lighting parameters. Gemstones graded between D-F are considered colorless, those between G-J are considered near-colorless, the ones from K to M are slightly colored, and N-Z usually appear light yellow or brown. The master sets used are precisely crafted and known as Cubic Zirconia.


They vary in colors like yellow, pink, red, blue, green, brown and many other tints due to variety of impurities and structural shifting. Whenever there is unusual intense saturation of colors, the diamond is termed as fancy colored. Though there are rating systems for such diamonds, because of their vast variation, no common grading system exists. Basically, they are classified into two types based on the impurity involved.

1. Type I Diamond - The main impurity is of nitrogen at a concentration of around 0.1%. They are further classified into IaA, where their structure is characterized by the presence of nitrogen pair bonded with carbon atoms. IaB represents those, which are characterized by even number of nitrogen atoms. They lead to produce yellow to brown tint. IaA and IaB are collectively known as cape series. When nitrogen is not present in a pair but scattered around the structure, the type is known as Ib, which gives intense yellow colorization to the diamond. They are characterized by visible absorption spectrum and have a typical fluorescence.

2. Type II Diamond - They carry less nitrogen impurities. With colors like pink, brown, and red, their formation is a result of plastic deformation and it is very rare. In Type IIb color varies from blue to gray, due to the presence of hydrogen or boron scattered within a matrix of crystal.

Factors Affecting Color

Parameters like fluorescence, enhancement techniques like HPHT and irradiation, affect the color of a diamond.
  • Fluorescence: It creates a major coloring effect, positive or negative, in presence of light. Virtually all exhibit this property in the presence of X-rays or UV rays. This characteristic also helps in identification of diamonds. Fluorescence if strong, may alter the perceived color of the given diamond positively or negatively. Hence, the gemstone which has no effect with fluorescence is rated higher.
  • HPHT (High Pressure/High Temperature) - It is a color enhancing treatment developed primarily by GE. An annealing process which involves high pressure and temperature, can change low color or fancy brown color gems to colorless gems. The change is permanent and can yield less expensive gems.
  • Irradiation- This process is carried out with the help of linear accelerator in combination with heating to produce fancy colored diamonds.
While making a purchase, you should always look for the graded color parameters. Colorless or near colorless ones are most expensive while others are less expensive.