Diamond colour

The scale grades how much yellow, brown or grey a white diamond shows. It starts at D for colourless and ends at Z for light yellow, light brown or light grey, and each letter in between marks a step with a defined range of appearance. GIA introduced the D-to-Z scale in 1953 to replace a muddle of letters, numbers, Roman numerals and terms such as “blue white”. The scale starts at D, not A, on purpose, so that it carries no link to the older systems.

Colour is one of the 4Cs. Colourless diamonds are scarce, since most diamonds have tints of yellow or brown, and that rarity is why the colourless end costs more. It also says many colour distinctions are so subtle that an untrained eye cannot see them.

Colour is judged by eye, but not casually. The right way to evaluate it is under controlled lighting, with the stone compared against master stones that have established colour grades. AGS describes a similar method: a grader places the diamond next to a master set and decides the grade from the strength of the colour.

AGS also notes that graders grade diamonds loose, with no setting, so that the metal cannot influence what they see. That matters when you shop, because the grade on a report describes the bare stone. It does not describe how the stone will look in your ring.

AGS uses its own numbers rather than letters, from 0 for colourless to 10 for light yellow or brown, and calls 0 to 1.0 its highest grades. Because the two systems use different scales, check which laboratory graded a stone before you compare two reports.

Stones in AGS’s near-colourless range, 1.5 to 3.0, appear colourless once mounted in jewellery. On GIA's scale, the near-colourless band is G to J. Near colourless is a common place to start looking if you want a white appearance without paying for the top of the scale.

Three things change the answer.

• Metal. A diamond set in a yellow-gold ring can look less yellowish than one in a white-metal mounting. A slightly warmer grade in yellow gold can therefore read as natural, while a diamond set in white gold or platinum shows its own tint more plainly.
• Shape. Brilliant cuts can make colour less noticeable by maximising sparkle and light return, while step cuts such as the emerald cut have larger facets that show colour more, so a buyer who wants a white step cut may need a higher colour grade.
• Neighbouring stones. In an all-diamond three-stone ring, GIA suggests keeping side stones within about two colour grades of the centre stone. Much whiter side stones make the centre stone look more yellow by comparison.

Not necessarily. The grades measure how little tint a stone has, and less tint is rarer, but taste varies. Many people prefer the look of a diamond with a slight yellow colour because of its warmth. If you want a white look, aim for the bands above. If you like warmth, a lower grade in a yellow-gold setting can be a deliberate and good-looking choice, and it frees budget for cut or carat weight.

The best test is a side-by-side look at two or three stones in a setting like yours, in daylight as well as indoor light. Photographs can shift colour, and the letter alone will not tell you which one you prefer.

The D-to-Z scale covers diamonds that are meant to look white. GIA uses “fancy colour” for any diamond with colour outside that normal range, typically yellow or brown stones with more colour than a Z master stone, or stones in other colours. A D-to-Z letter does not describe them. See the entry on fancy coloured diamonds.

If you are choosing a white diamond for a custom ring, a jeweller can talk through how the metal and setting will change the colour you see. The custom engagement rings service starts from the shape, setting and stone you prefer.