Color grades are not absolute. Two diamonds with the same grade can appear very different, depending on which labs did the grading, cut quality, shape, size and other important particulars. Since we don’t wear a tag boasting the color of the diamond it’s important to know what factors may influence the color a viewer will see.

Laboratory Grading

It’s most important to know that laboratories don’t enforce the same standards. Diamonds graded by the AGS and GIA are held to the highest and most consistent standards, but you might not be comparing apples to apples when looking at diamonds graded elsewhere: An F from a second tier lab may actually be a G or an H if GIA standards were enforced. In fact many commercial sellers purposely send their diamonds to a softer lab because the ‘paper’ looks better. This means they can sell average diamonds for higher prices. This applies to clarity and cut as well (read more).

Cut Quality

Diamonds in the D-Z range are color-graded upside down, viewed from the side. This is because the way a diamond is cut may have an influence on face-up color. Diamonds can be cut for top light return, where almost all light entering the crown reflects from the pavilion at precise angles back to the viewer’s eyes. Such well-cut diamonds entrap less body color and have increased brilliance, dispersion and scintillation. This is most observable in premium rounds because their circular shape and brilliant faceting style maximize light return and performance qualities. Rounds in the top few percent of the world’s cut quality often appear more colorless face-up than their lab-assigned grade.

Different Shapes

Some shapes other than round may benefit from cut quality as well. The princess incorporates aspects of the brilliant style, so its face-up appearance can be positively influenced. Step cuts like the emerald have longer facets and show less color at shallow depths. Their face-up appearance can be influenced by cut but not as much as shapes with brilliant faceting. The design of the radiant entraps body color more than other shapes. While it’s possible to cut a radiant so that it doesn’t entrap color the style in general is conducive to showing color. This is why many fancy colored stones are cut as radiants. The corners and shoulders of fancies may show color more than the center of the stone. This is because those areas don’t benefit from improved light return as much as the body of the shape does.

Fluorescence

The GIA conducted a 1997 study showing fluorescence is a non-factor in most diamonds and in others it helps face-up appearance. Medium blue fluorescence and stronger may be a benefit to near-colorless diamonds (GHIJ) and below. Fluorescence of a color other than blue should be questioned as it will not usually help color appearance unless in a diamond is of the same color. Strong or very strong fluorescence can give a soft hazy ‘glow’ in sunlight, which some enthusiasts seek for its appeal. A tiny percentage of diamonds with very strong fluorescence appear milky or oily, but this is rare. Always consult a professional who has the diamond in-hand with questions.

Size

Large diamonds have greater body volume and logically show more color than their smaller counterparts, especially as color gets lower. Premium cut quality can benefit larger stones.

Cleanliness

Diamonds are natural grease attracters. A dirty pavilion changes a diamond’s appearance, so once handled by several people it may not be at its best. Over time dirt and even metal from tweezers can become lodged in bruted girdles. Shoppers don’t need to worry about this, but appraisers may one day find their bruted master stone set is in need of an acid boil (the only way to clean a dirty bruted girdle).

Lighting & Environment

Jewelry store spotlights are not good for color and clarity judgments. Subtleties of color, along with any fine tuning of the cut, are overwhelmed by the sheer volume of light coming from the stone. To judge color realistically a diamond must be removed from direct lighting. A practical environment for assessment is diffuse lighting, such as the fluorescent lights found in office buildings. Remember that diamonds absorb the color of their surroundings. This is why diamond graders wear white lab coats and grade against a white background under fluorescent tubes.

Setting

One mounted a diamond will show less color than it did loose. Remember that the choice of setting may influence your diamond’s color. If you choose a gold setting and have a colorless diamond the diamond may absorb and reflect back some of the setting color.

Human Perception

There are 23 descending color grades and the increasing hints of color are very slight. When diamonds are mounted and dynamic it becomes very hard to differentiate between several colors. All else being equal, the difference between one or two grades is not noticeable to most humans. Of course, the ability to perceive differences varies among people and can be influenced by such things as fatigue and even the yellowing of one’s corneas with age. Differences are even harder to see when the diamonds are mounted and worn. Diamonds a few color grades apart, identical in all qualities except color, may be indistinguishable when worn separately. Even the most color sensitive person may not detect a difference unless they are set next to each other in neutral lighting and studied closely.

Color and Pricing

Although descending color grades are subtle price differences are not. They jump most notably when you cross the line from near-colorless to colorless. The reason for the price jump is not necessarily because of a visible difference; it is because colorless diamonds are more rare, so you're paying for the rarity, not a "better" looking diamond.

To some people one or two grades matters a lot. To others, it matters not at all. Color and clarity tolerances are very personal, subjective matters - with no wrong decisions.

The Internet and Color

If you’re shopping on the internet you can’t make color determinations with imagery or photos. It may be possible to see how diamond A appears in direct comparison with diamond B (as long as they are side by side in the same photo against a neutral background) but decisive judgments are impossible due to differences in camera settings, monitors and software. It’s best to speak with a trusted expert who has the diamond in hand to tell you reliably how the diamond appears.

Artificial Color Enhancement

Artifical color enhancement, or High Pressure High Temperature treatment (HPHT) is a process where a diamond is irradiated to improve its color. Many sellers trade only natural diamonds and do not deal in those with color or clarity enhancements. Sellers who do are required to disclose the fact that they were so treated.

Fancy Colors

Unlike diamond on the D-Z scale, fancy colored stones are graded face-up to best judge their hue, tone and saturation. Also different is the fact that such stones are cut to ENTRAP as much body color as possible. Many colored stones are cut in square shapes and fancy colored round diamonds typically have proportion sets steeper or shallower than commonly agreed on ‘ideal’ proportions. This causes light to pass through the stone, nicely illuminating the color but not washing it out. This is why top cutters caution against steep/deep combinations in D-Z shapes: In addition to appearing smaller for their weight, such proportions sets entrap body color more readily.