The presence or absence of color has a significant effect on a diamond's overall look and value. Using the standard set by the Gemological Association of America, a diamond is graded for color according to its degree of colorlessness. A diamond's color is permanent and is a result of its composition as the rough crystal grows.

Color is graded according to the following color scale and criteria:

• D - Complete absence of color, this is the benchmark against which all other colors are graded
  
• E-F Colorless - These diamonds are extremely rare and valuable because they possess a minute trace of color which can only be detected by a trained professional.
  
• G-H Near Colorless - While these diamonds possess no color that is visible to the untrained eye, they possess a hint of color only detectable when compared against the "D" color.
  
• I-J Near Colorless - Color is slightly detectable, but these diamonds are an excellent value.
  
• K-L Slightly Yellow - These diamonds may look slightly more yellow compared to those of higher rating, however in most cases, mounting these diamonds in yellow gold masks their color making them look more colorless.
  
• M-Z Yellow - Diamonds in this range have a definite yellow or brown cast which is not considered attractive or marketable in jewelry.
  

Fancy Color Diamonds

Although most diamonds fall into the color scale ranging from D-Z, a very rare few fall into the "Fancy Color" category that cannot be graded using the traditional scale. These diamonds are extremely rare and very precious and can come in colors such as red, blue, green, pink, and bright yellow. Their relative value is assessed according to the depth and saturation of color as well as their rarity.

Fluorescence

Fluorescence is an effect seen when a diamond is exposed to ultraviolet light. Although invisible in most lighting conditions, a diamond's fluorescence will emit a yellow or blue glow when held under UV light. In diamonds with no hint of yellow, the presence of strong fluorescence may affect the diamond by showing a milky or cloudy appearance; however in diamonds that are slightly yellow, the fluorescence may actually make the diamond look more colorless. The fluorescence of a diamond is rated on a diamond report as Strong, Medium, Faint, or None.

• Look for a diamond in the D-F range with little or no fluorescence. An otherwise high quality diamond in this color range which has medium or strong fluorescence will have less sparkle and be valued and priced lower.
• Diamonds in the Near Colorless, G-J grades provide an excellent value for their look. These diamonds have no noticeable color to the unaided eye and the presence of fluorescence will not have a significant effect on the overall brilliance.
• If you choose to wear yellow gold jewelry, and would like to keep your selection under budget, consider J-K range for color. These colors will be very noticeable in white gold or platinum, however will not be as visible in yellow gold. Compromising a bit on color may allow you to purchase a larger diamond and still keep your selection within your budget.