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Natural Fancy Colour Diamonds: Colours, Grading and Rarity

By the Byrex Gems team, Toronto · Published 25 September 2026

What causes colour in diamond, how GIA's fancy colour grades work, why cut and modifiers matter, how rare each colour is, and how laboratories separate natural, treated and laboratory-grown stones.

Most diamonds are judged by how little colour they show. Natural fancy colour diamonds are judged the other way round: by the presence, strength and purity of their colour. GIA defines a fancy colour diamond as one whose colour falls outside its D-to-Z scale, and GIA research has put the rarity of fancy colour at roughly one carat in every 10,000 carats of polished diamond. This guide explains what causes colour in diamond, how GIA grades it, why cutting matters, how rarity differs from one colour to another and how laboratories separate natural colour from treated and laboratory-grown stones.

What causes colour in a diamond

Pure diamond is colourless. Colour comes from small departures from a perfect carbon lattice: trace elements such as nitrogen, boron or hydrogen, distortion of the crystal structure, or damage from natural radiation. Gemmologists also sort diamonds into "types" by their nitrogen and boron content. According to GIA, about 95 per cent of natural diamonds are Type Ia, with nitrogen atoms grouped in clusters. Type Ib diamonds contain isolated nitrogen atoms and are extremely rare. Type IIa diamonds have no measurable nitrogen or boron, and Type IIb diamonds contain boron and conduct electricity.

Yellow
Main cause: Nitrogen
Notes from GIA research: About 74% of fancy yellows owe their colour to aggregated nitrogen ("cape" defects, Type Ia); about 13% to isolated nitrogen (Type Ib), the classic bright "canary" colour.

Orange
Main cause: A defect absorbing near 480 nm
Notes from GIA research: Responsible for about 86% of pure orange diamonds; isolated nitrogen accounts for most of the rest.

Blue
Main cause: Boron (Type IIb); hydrogen-related defects
Notes from GIA research: Boron was the cause in 35% of a GIA sample of blue, grey and violet diamonds; hydrogen-related defects in 30%, mostly from the Argyle mine.

Pink, red, purple
Main cause: A band near 550 nm linked to plastic deformation
Notes from GIA research: The exact atomic defect is still unidentified, but it is associated with deformation of the crystal lattice. Colour often lies in narrow parallel bands known as graining or lamellae.

Green
Main cause: Natural radiation (GR1 vacancies); also H3 and hydrogen defects
Notes from GIA research: Radiation damage from nearby radioactive minerals accounted for about 34% of green diamonds examined; the colour is often a shallow skin that can be lost in cutting.

Brown
Main cause: Plastic deformation (vacancy clusters)
Notes from GIA research: The most common fancy colour.

Grey, violet
Main cause: Hydrogen-related defects; micro-inclusions
Notes from GIA research: Hydrogen-rich greys and violets are strongly associated with Argyle.

Two findings stand out. GIA scientist Evan Smith and colleagues reported in Nature in 2018 (see GIA's review of blue diamonds) that boron-bearing Type IIb blue diamonds form at superdeep levels, more than 600 kilometres down, and estimated that they make up only about 0.02 per cent of mined diamonds. And in a study of more than 90,000 natural pink diamonds graded between 2008 and 2016, GIA confirmed the link between pink colour and plastic deformation in the vast majority of stones, while noting that the precise defect has not yet been identified.

How GIA grades fancy colour

GIA describes a coloured diamond's colour by three attributes: hue, the colour itself; tone, its relative lightness or darkness; and saturation, its strength or depth. GIA recognises 27 hues for fancy colour diamonds. A trained grader views the diamond face up, under controlled lighting and viewing conditions, and compares it with colour reference stones. GIA expanded its system in the mid-1990s, adding the terms Fancy Deep and Fancy Vivid.

The result is one of nine grade terms combined with the hue, for example "Fancy Intense Yellow" or "Fancy Vivid Purplish Pink".

Faint, Very Light, Light
What it describes: The lightest descriptions. GIA found that 54% of the unmodified pink diamonds in its large study fell into these three grades.

Fancy Light, Fancy
What it describes: Increasing strength of colour.

Fancy Intense, Fancy Vivid
What it describes: Stronger, more saturated colour; GIA notes these grades generally command higher prices.

Fancy Dark, Fancy Deep
What it describes: Descriptions for colour that is darker in tone.

GIA's own lists order the terms slightly differently in different publications, but the principle is consistent: the grade describes the combined effect of tone and saturation, and it is assigned from the face-up appearance of the whole stone. Yellow and brown diamonds with only a small amount of colour are graded on the D-to-Z scale; a stone becomes a fancy colour once it moves beyond that range.

Hue and modifiers

Few coloured diamonds show a single pure hue. In GIA's pink study, 40% of the stones were described as unmodified pink; the rest carried modifiers such as purplish, brownish or orangy. In a GIA colour description, the modifying colour comes first and the dominant hue last: a "purplish pink" is predominantly pink with a purple influence.

Modifiers affect value. GIA notes that pure yellow diamonds are rarer and more desirable than those with brownish or greenish modifiers, although a touch of orange can add warmth. A modified colour can still reach the very top of the market, however: the Eternal Pink, graded Fancy Vivid Purplish Pink, sold for $34.8 million at Sotheby's New York in June 2023.

How shape and cutting affect colour

For colourless diamonds, cutters aim to maximise brilliance. For coloured diamonds, GIA explains that stones are usually cut to maximise the intensity of face-up colour rather than light return, and that the best cut is the one that gives the most attractive face-up colour. Several practical points follow:

  • Mixed cuts intensify colour. GIA notes that radiant cuts in particular can concentrate yellow, so that a lightly tinted rough may be graded a fancy yellow once cut.
  • Path length matters. Larger stones and deeper pavilions give light a longer path through the diamond, which often produces richer colour.
  • Round brilliants are less common in coloured diamonds. GIA's guidance on yellows notes that the high light return of a round brilliant can dilute body colour, which is why cushions, radiants, ovals and pears dominate.
  • Orientation matters for pinks. Where colour is concentrated in lamellae, cutters orient the stone to show the most colour through the table.

Relative rarity by colour

GIA ranks browns and yellows as the most common fancy colours, and red, green, purple and orange as the rarest. Its research gives some scale to this:

  • Yellow is the largest fancy colour category submitted to GIA, with several hundred thousand stones examined.
  • Green diamonds made up less than 0.07% of all diamonds examined by GIA in its green study.
  • Blue diamonds coloured by boron represent about 0.02% of mined diamonds, and most come from the Cullinan mine in South Africa.
  • Red is so rare that GIA reports it issued no reports describing a diamond as pure red, without a modifier, between 1957 and 1987.
  • Pink diamonds are also small on average: in GIA's study, 83% weighed under one carat.

The Argyle mine and pink diamonds

Rio Tinto's Argyle mine in the Kimberley region of Western Australia began operating in 1983 and produced about 865 million carats of rough over its life. Although most of its output was brown, it became famous as the source of the great majority of the world's pink diamonds; the ABC reported the figure as 90 per cent, and Sotheby's puts it at around 80 per cent of recent production. GIA's own study found that at least 43% of the pinks it examined showed the characteristics of Argyle material, and that pinks represented much less than 0.1% of the mine's production.

Mining at Argyle ended on 3 November 2020. For close to four decades, Rio Tinto sold the best pink, red and blue diamonds each year through the invitation-only Argyle Pink Diamonds Tender, typically 50 to 60 stones. The final tender, held in 2021 under the title "The Journey Beyond", offered 70 pink and red diamonds and 41 lots of blue diamonds; its five hero stones were led by the 3.47-carat Argyle Eclipse, graded Fancy Intense Pink. Writing before the closure, GIA researchers expected the supply of saturated pinks and reds to decline once Argyle stopped producing. For collectors, an Argyle provenance now marks a stone as part of a finite supply.

Natural, treated and laboratory-grown

The same colours that occur in nature can be produced or enhanced artificially, which is why a laboratory report is essential for any fancy colour diamond.

  • Treatments. GIA lists irradiation, annealing, HPHT (high-pressure, high-temperature) processing and coating as the main colour treatments. HPHT can turn brownish diamonds yellow or green and can enhance pink in suitable pinkish-brown diamonds; irradiation can produce a range of colours, and irradiation combined with heating is used to turn pale brown or very light diamonds pink. GIA notes that most black diamonds are treated. It issues reports only for stable treatments, laser-inscribes the girdles of diamonds it identifies as colour-treated, and will not issue a report for a coated diamond.
  • Laboratory-grown. Coloured laboratory-grown diamonds are produced by HPHT growth (boron for blue, nitrogen for yellow) and by CVD growth followed by treatment. GIA laser-inscribes commercial-size laboratory-grown diamonds it examines with "LABORATORY-GROWN".
  • How GIA tells them apart. Identification relies on a combination of evidence: infrared and photoluminescence spectroscopy, deep-UV fluorescence imaging with the DiamondView, photoluminescence mapping and microscopy. Examples from GIA research include the absence of cape defects and the 480 nm band in most laboratory-grown diamonds, a band near 520 nm rather than 550 nm in some CVD-grown pinks, and growth patterns revealed by DiamondView imaging that separate natural from synthetic blues.
  • The hardest case is green. GIA notes that laboratory irradiation takes only minutes and that the spectra of natural and treated green diamonds are virtually identical in many cases, which can make colour origin extremely difficult to determine.

GIA also cautions that no rapid, low-cost screening device can definitively identify every laboratory-grown diamond, and that conclusive identification usually requires full laboratory testing. GIA's Colored Diamond Grading Report records the colour grade, colour origin, clarity and cutting details; its Colored Diamond Identification and Origin Report covers colour grade and colour origin.

What drives price

  • Hue. GIA identifies saturated pinks, blues and greens, and reds, as the most prized colours; yellows and browns are more plentiful and priced accordingly.
  • Grade term. Fancy Intense and Fancy Vivid generally command higher prices than lighter grades.
  • Modifiers. Secondary colours change desirability; GIA notes, for example, that pure yellows are rarer and more desirable than brownish or greenish yellows.
  • Size. GIA notes that large fancy colour diamonds are rarer and more valuable than small ones.
  • Clarity and cut. Colour dominates value, and GIA notes that even included stones can command high prices if their face-up colour is attractive.
  • Colour origin and provenance. A report confirming natural colour is fundamental. Provenance matters too: Rio Tinto reported that Argyle pink diamonds appreciated by more than 500 per cent over two decades.

At the top of the market these factors combine dramatically: the 11.15-carat Williamson Pink Star, graded Fancy Vivid Pink and Internally Flawless, sold at Sotheby's Hong Kong in October 2022 for $57.7 million, over $5.1 million per carat. Our companion article on record auction sales sets out the benchmark results in detail.

To discuss natural fancy colour diamonds accompanied by laboratory reports, please email info@byrex.com or send a WhatsApp message to +1 (437) 450-3786.

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