It is the absence of color that gives a diamond its high value. If any color is detected, even if it is only slight, the diamonds value is affected; However there are diamonds that are valued for the presence of color for example "fancy" diamonds which come in a variety of colors are valued depending on their color the most rare color in diamonds is red.

Diamond color grades range from D to Z however only colors ranging between D through M are considered to be in the standard color range. Diamonds whose color is graded between D and F are naturally the most valuable since they are much harder to find because of their rarity. Diamonds graded between G and I, do not have any visible color that can be seen by the untrained eye. Diamonds that are graded J through M, have visible yellowish color that can often be almost completely hidden by deliberately choosing the right color setting and mounting style. For example, yellow gold will hide and decrease the visibility of any traces of yellowish color in a colorled diamond, however platinum and white gold settings make it more visible.

Diamonds that are within the standard color range can show slightly perceptible to light yellowish or brownish hues and sometimes gray. Diamond whose color ranges outside the standard color scale such as Z+ are called fancy colors and have a different grading and pricing scale. Diamonds with faint or vivid hues such as blue, yellow, or pink, are usually used for very expensive fashion jewelry.

Most times people who considering to buy a diamond, are looking for a stone in the standard color range these diamonds are the ones commonly seen in diamond jewelry. Diamonds without any color whatsoever such as D or E are very rare and therefore highly expensive. Rarity and in that case price get lower as the range of color goes down towards  Z. The difference between D-E color diamonds and H-I color diamonds are basically invisible to the untrained eye. In order to accurately assess color grading, a diamond must be checked with its top facet face down under strong lighting and a white background. The ability to accurately grade color is highly diminished when a diamond is set into jewelry, that is why the renowned gemological diamond grading laboratories grade only loose diamonds.

Fancy color diamonds color is measured totaly differant  the paremeters turn to the purity and richness of the specific diamond's color. Yellow is the most commonly found fancy color. Red and green diamonds are very hard to find and are extremely rare. The price of fancy colored diamonds depends on a few  factors the very particular hue of the diamond the more rare that  the color is the the more expensive it is. Richness of the color ranging from very light to vivid, and the purity of the color which means if the color is clear and bright, or 'dirtied' by the visibility of another color causing other color elements.

FLUORESCENCE

Almost thirty five percent of all gem quality diamonds glow or fluoresce when they are exposed to what is called "ultraviolet  radiation(UV)". This happens when a diamond's atomic structure meets with energy of the UV's radiation. A lot of  diamond owners may notice the fluorescent in their diamond when they are exposed to strong light or under the  lights of a nightclub. The color of fluorescence is usually blue, but some diamonds can also show fluorescence in different colors such as white, green, yellow, red or orange.

GIA describes the different levels of fluorescence with the following terms: None, Faint, Medium, Strong and Very Strong. The AGS describes fluorescence levels using other terms: Negligible, Medium, Strong and Very Strong. Until not long ago, the AGS described using the terms of "Inert" and "Faint", but were recently changed to a single descriptor "Negligible."

Fluorescence does not really have much affect on a diamond's appearance under regular light conditions. Diamonds in 'I through N' color range, strong blue fluorescence actually help improve the look and appearance of the stone by  few color grades. This happens because blue and yellow are opposite colors  and erase each others affect. It is very important to note that in some instances  Strong to Very Strong fluorescence can make a diamond look cloudy or oily in especially strong sunlight or other extreme ultraviolet light conditions.

In the last few decades the diamond market has changed its attitude on the issue of fluorescence. In the early 1970s, fluorescence was accepted as an special bonus - sometimes people would wake their children and call the neighbors about. Back then you might expect to pay more for a fluorescent diamond. In the late 1980s and early 1990s tastes changed and fluorescence took on a slightly negative connotation. The market quickly reflected this change and diamonds in the higher color ranges with strong fluorescence today often sell for a 10-15 percent discount.