Natural coloured diamonds are diamonds that get a distinct hue, such as yellow, pink, blue or green, from natural processes inside the earth, with no colour added in a lab. The trade calls them fancy colour diamonds, and you will also see the US spelling "natural colored diamonds". A white diamond loses value as colour creeps in. A coloured diamond gains value as its colour gets stronger, and only about one in 10,000 carats of fashioned diamonds shows fancy colour at all.

This guide covers what you need before you shop. You will see why these stones are rare and how their value works, which colours exist and what causes each one, how a laboratory grades colour, and how to buy a genuine stone without overpaying or getting a treated one by mistake.

We design bespoke engagement rings in Hatton Garden, and a coloured centre stone is one of the choices a ring can be built around. The more you know about colour, intensity and certification, the better your decisions will be when you reach the design stage.

Why natural coloured diamonds are rare and valuable

Natural coloured diamonds are valuable because they are extremely scarce, and because their price rises with the strength of the colour instead of falling with it. Understanding both ideas explains almost every price you will see.

Rarity in numbers

According to the Gemological Institute of America (GIA), only one in 10,000 carats of fashioned diamonds shows fancy colour. The chance of strong, intense colour is lower again, at one in 25,000. Put another way, in a parcel of 100,000 polished carats you would expect around 10 carats of fancy colour and only 4 of intense colour.

Rarity also varies by hue. Browns and yellows are the most common fancy colours, while red, green, purple and orange are the rarest. Only a handful of red diamonds larger than 5 carats have ever been found.

A coloured diamond is priced on how rare and how strong its colour is, not on how little colour it has.

How value works

Colourless diamonds are graded on the D to Z scale, and value drops as a yellow or brown tint becomes visible. Fancy colour diamonds sit beyond that scale and follow the opposite rule. These factors move the price most:

• Colour intensity: Vivid and intense grades command the highest prices.
• Colour purity: A single clean hue, such as pure orange, is rarer than a stone with secondary tones.
• Size: Large stones of strong colour are exponentially harder to find.
• Origin: Stones from closed sources, such as Australia’s Argyle mine for pinks, can carry a premium.

Prices span a very wide range. Pale yellows and browns can cost roughly what a white diamond of the same size does, while a vivid pink or blue can cost many times more per carat.

The colours that occur naturally and what causes them

Natural diamonds occur in almost every colour, and each one has its own cause, which also explains why some are far rarer than others. The table sets the main colours side by side.

Colours, causes and rarity

Grey diamonds also exist, often caused by boron or hydrogen. Notable examples include the Hope Diamond for blue and the 41 carat Dresden Green.

Why the cause matters to you

Yellow and blue come from chemical impurities, but pink and red come from a structural distortion in the crystal. That is one reason a pure pink or red is so hard to find. Black diamonds are different again. They are coloured by mineral inclusions that block light, so they look opaque and metallic instead of transparent.

Green deserves extra caution. Radiation turns a diamond green naturally when a deposit sits near radioactive rock, but laboratories can also irradiate a diamond to do the same. Because of that, green stones are examined very carefully, and even advanced testing cannot always settle the origin of the colour.

The more dramatic and rare the colour, the more important it is to prove that it is natural.

How natural coloured diamonds are graded

Coloured diamonds are graded for the hue, tone and saturation of their colour, and the result is a named intensity grade on a laboratory report. GIA’s system is the standard, and virtually every coloured diamond sold at major auction houses has been graded by GIA.

Hue, tone and saturation

Hue is the main colour, tone is how light or dark it looks, and saturation is how strong it is. Coloured diamonds come in so many shades that no complete set of master stones could cover them. GIA therefore uses a mix of comparison stones and printed standard colours to find a diamond’s characteristic colour, then assigns an intensity grade.

The intensity scale

GIA reports use these colour grades:

• Paler end: Faint, Very Light and Light.
• Main fancy grades: Fancy Light, Fancy, Fancy Intense and Fancy Vivid.
• Darker tones: Fancy Dark and Fancy Deep.

Fancy Vivid is the most saturated of the main grades and usually the most prized. A balanced tone matters, because a stone that is too dark or too pale loses impact even when the hue is right.

Reading a report

A grade often includes a secondary hue, as in "Fancy Intense purplish pink", where pink is the main colour and purple a modifier. A single clean hue is generally worth more than a mixed one. Check the report for the colour grade, the stated origin of colour and any note of treatment. Colour carries most of the value, so cut and clarity matter, but they come second.

The report is the stone’s identity: no independent grade, no confident price.

How to buy a natural coloured diamond with confidence

Buy on a report, not on a photograph. Whether you are comparing natural colored diamonds for sale online or in a showroom, the same checks protect you.

A checklist before you commit

1. Set a colour and intensity target. Decide on the hue and the grade, such as Fancy Intense yellow, before you look at prices.
2. Ask for an independent laboratory report. GIA is the benchmark, and the report should state that the colour is natural.
3. Check for modifiers. Secondary hues change the price, so compare like with like.
4. Ask about treatment in writing. Irradiation, high-pressure high-temperature (HPHT) processing and coatings can all change colour, and treated stones are worth far less than natural ones.
5. See the stone in several lights. Daylight and indoor light can make a pale colour look different.
6. Arrange insurance. A stone of this value should have a valuation certificate for insurance.

Natural, treated and lab-grown

A treated stone is a natural diamond whose colour has been altered. A lab-grown coloured diamond is a real diamond grown in a laboratory, with the same look as a mined one at a lower price, though it is not rare. Neither is wrong, but each should be sold as what it is. A Star Diamonds offers both natural and lab-grown diamonds, so you can compare them against your budget.

Turning the stone into a ring

A coloured diamond changes how a ring should be designed, because the setting needs to protect the stone and show its colour. Our complimentary consultation, in person at Hatton Garden or online, is the place to bring your colour ideas and your budget. Every ring is made by hand to your design, and lifetime free resizing, polishing and cleaning are included.

What to remember about natural coloured diamonds

Natural coloured diamonds are rare because their colour comes from chemistry or crystal distortion that few stones ever experience. They are valuable because intensity, purity and size all raise the price. They are graded by hue, tone and saturation, and the grade sits on an independent report that should also confirm the colour is natural.

If you are considering a coloured centre stone for an engagement ring, start with the colour you love, set a budget and insist on certification. When you are ready to turn the idea into a design, book a consultation with A Star Diamonds and talk through your options with our team.