Kove Jewelry

Coloured lab-grown diamonds: pink, blue, yellow and green

Updated 17 October 2026. By Alexey Kovernikov, owner of Kove Jewelry in Prague.

A pink or blue diamond used to be something you saw in an auction catalogue, not in an engagement ring. Lab-grown diamonds changed that. But a coloured stone raises questions a white one does not: where does the colour come from, was it added after growth, will it last, and what exactly does the certificate say? This guide answers those questions with what GIA and IGI publish — and with what we see in the stones available to Kove.

Where the colour comes from

A colourless diamond is pure carbon in a perfect lattice. Colour appears when something in that lattice absorbs part of the light — a trace element or a structural defect. The same causes apply to natural and lab-grown diamonds; the difference is whether nature or a process put them there.

Colour	What causes it	In lab-grown stones
Yellow	Nitrogen atoms in the crystal absorb blue light.	Common as grown: GIA notes that most HPHT-grown diamonds are yellow to orange, depending on how much nitrogen gets in.
Blue	Boron in the crystal (natural type IIb diamonds).	Growers deliberately add boron in HPHT growth, which gives blue crystals. Blue can also be produced by treatment.
Pink / red	In nature: believed to be plastic deformation of the lattice deep in the earth.	GIA: pink and red can be produced by post-growth treatment — for example HPHT processing, irradiation and low-temperature annealing.
Green	Radiation knocks carbon atoms out of place (the GR1 defect), in nature or in a laboratory.	Laboratory irradiation has been used to create green since the late 1940s and closely mimics the natural effect.

Sources for each line are listed at the end of this guide (GIA Gems & Gemology and GIA 4Cs).

HPHT and CVD: two ways to grow — and why treatment is so common

HPHT (high pressure, high temperature) recreates the conditions deep in the earth: a diamond seed, a carbon source and a molten metal flux, heated to 1,300–1,600 °C under enormous pressure. Because nitrogen and boron end up in the crystal easily, HPHT is the natural home of as-grown yellow and blue lab-grown stones.

CVD (chemical vapour deposition) grows diamond layer by layer from a carbon-rich gas plasma onto a seed at about 900–1,200 °C. GIA notes that CVD crystals often come out brownish, and that CVD now dominates the lab-grown diamonds submitted for grading — roughly 80% of them have had a post-growth HPHT treatment to improve their colour.

For fancy colours the same logic applies: a stone is grown, then often treated to reach the exact pink, red or green. That is normal, legal and stable — as long as it is disclosed. It is disclosed on the report.

What the certificate says — the exact lines to look for

In our sample (below), about 98% of coloured lab-grown stones were graded by IGI. On an IGI Laboratory Grown Diamond Report, look at three places:

Color Grade — the hue with its Fancy grade, for example "FANCY VIVID PINK". IGI’s report prints the scale it uses: Fancy Light, Fancy, Fancy Intense, Fancy Vivid.
Comments, growth method — "This Laboratory Grown Diamond was created by Chemical Vapor Deposition (CVD) growth process" or "… High Pressure High Temperature (HPHT) growth process".
Comments, treatment — either "As Grown - No indication of post-growth treatment." or "Indications of post-growth treatment." Sometimes a secondary colour is noted too (for example "Secondary color: Brown").

GIA, for its part, has said its laboratory-grown reports state whether a stone was created by CVD or HPHT and whether it may include post-growth treatment to change the colour. For natural coloured diamonds, every GIA report states whether the colour is natural or treated.

Treated does not mean fake or worse. It means the colour was finished after growth. What matters is that the line is there, that you have read it, and that the price you are offered reflects what the stone is.

Fancy colour grades in plain words

Coloured diamonds are not graded D to Z. GIA describes colour by hue (the colour itself), tone (how light or dark) and saturation (how strong), and combines tone and saturation into one "Fancy" grade. GIA lists the grades in order of increasing colour strength: Faint, Very Light, Light, Fancy Light, Fancy, Fancy Intense, Fancy Vivid, Fancy Dark and Fancy Deep.

GIA notes that Fancy Intense and Fancy Vivid generally command higher prices, and that for coloured diamonds a more vibrant colour typically means higher value. A secondary colour in the name — "purplish pink", "greenish blue" — is part of the grade and changes how the stone looks.

Is the colour permanent?

GIA states that irradiation treatments are stable to regular wear, and that HPHT treatment is stable — which is why GIA grades such stones. The one known weak point is heat: GIA warns that irradiated diamonds may be more sensitive to the heat involved in repair procedures. In practice: before any repair or sizing work, tell the jeweller the stone is treated so it is protected or taken out of the setting first.

GIA has also described a temporary colour shift in some CVD-grown stones after strong UV light or heat, which is why its graders check colour stability on certain blue and grey CVD stones. Everyday wear and daylight are not the issue; the point is to know what you own and say so when the ring goes for service.

What is actually available: our sample

In a 10% sample of coloured stones in our partner supplier network on 17 October 2026, this is how the four colours split between lab-grown and natural:

Colour	Lab-grown stones	Natural stones
Pink	3,567	8
Yellow	2,883	185
Blue	2,261	3
Green	1,001	7

About 98% of the lab-grown coloured stones in the sample were graded by IGI (none by GIA); the natural ones mostly by GIA. Lab-grown pink outnumbered natural pink by more than 400 to one, blue by more than 700 to one. The natural side of the sample was dominated by black and yellow stones.

That is the honest reason natural pink and blue diamonds cost what they do: GIA counts saturated pinks, blues and greens among the rarest and most valuable diamond colours, and large ones are rarer still. A lab-grown stone gives you the same colour on a real diamond, with a report, at a size you can actually choose.

Buying checklist for a coloured centre stone

Ask for the report and verify the number on the lab’s website (igi.org or GIA Report Check).
Read the Comments: growth method, and the treatment line — "As Grown" or "Indications of post-growth treatment".
Read the full colour name, including any secondary colour ("purplish", "brownish", "greenish").
Ask for a daylight video, not just studio photos. Coloured stones change more between light sources than white ones.
Balance intensity against size: a lighter grade can look pale in a small stone, a deeper grade can look dark in a large one. Judge the video, not the grade alone.
For a natural coloured diamond, check that the report says natural colour — and expect a very different price.

Choosing a coloured lab-grown stone for a Kove ring

Every Kove engagement ring is made to order with a centre stone chosen individually — colourless or coloured, lab-grown or natural — in 14K or 18K white, yellow or rose gold. Every centre stone above 0.30 ct comes with its IGI or GIA report.If you already have a specific stone in mind, you can open it directly in the stone browser by its certificate number or stock ID. How to search by certificate or stock ID. Then pick a setting from the rings, or write to us and we will check the stone and the report with you before you order.

Frequently asked questions

Are pink lab-grown diamonds treated?

Usually the pink is created or finished after growth. GIA describes pink and red lab-grown colour as produced by post-growth treatment, for example HPHT processing followed by irradiation and low-temperature annealing. The IGI report says it plainly: "Indications of post-growth treatment" or "As Grown – No indication of post-growth treatment".

Do coloured lab-grown diamonds fade?

Not in normal wear. GIA states that irradiation and HPHT treatments are stable to regular wear. The caution is heat: irradiated diamonds may be sensitive to the heat used in jewellery repair, so tell the jeweller the stone is treated before any work on the ring.

Are blue lab-grown diamonds real diamonds?

Yes. A lab-grown diamond is carbon in the diamond crystal structure, just grown above ground. Blue lab-grown stones get their colour from the same element as natural blue diamonds — boron — or from a post-growth treatment, which the report discloses.

What does "Fancy Vivid" mean?

It is one of the strongest grades on the coloured-diamond scale. GIA combines a stone’s tone and saturation into one Fancy grade, listed in order of increasing colour strength from Faint to Fancy Light, Fancy, Fancy Intense, Fancy Vivid, Fancy Dark and Fancy Deep. GIA notes that Fancy Intense and Fancy Vivid generally command higher prices. On IGI lab-grown reports, Fancy Vivid is the top step of the printed scale.

Natural or lab-grown coloured diamond — how to tell?

Not by eye. GIA says conclusive identification needs a combination of laboratory features, not a single test. As a buyer, rely on the report: an IGI lab-grown report is titled "Laboratory Grown Diamond Report" and its number starts with LG; a GIA report for a natural coloured diamond states whether the colour is natural or treated. Check the number on the lab’s website.

Why are natural pink and blue diamonds so much more expensive?

Rarity. GIA counts saturated pinks, blues and greens among the rarest and most valuable diamond colours. In a 10% sample of coloured stones in our partner supplier network on 17 October 2026 there were 3,567 lab-grown pink stones against 8 natural ones, and 2,261 lab-grown blue against 3 natural.

Can I choose a coloured centre stone for a Kove ring?

Yes. Coloured lab-grown centre stones can be chosen for Kove rings. Find a stone by its certificate number or stock ID in the stone browser, or send us the number and we will check it with you.