# Diamond Colour Grade: G vs H, Gold Colour and Fluorescence

> What a diamond colour grade measures, whether you can see G against H, how white, yellow and rose gold change the look, and what fluorescence means.

Canonical: https://mazimo.ae/journal/diamond-colour-grade-and-fluorescence

Diamonds · Published 17 October 2026 · 10 min read · Mazimo Jewellery, Dubai

A diamond colour grade is a letter from D to Z that rates how little colour a stone has: D is colourless, and each later letter has a little more. A laboratory grades the loose stone with its flat top, the table, facing down, so the letter describes the diamond out of its ring. G and H sit side by side in the [near colourless group](https://4cs.gia.edu/en-us/blog/a-guide-to-diamond-color-d-to-z/) of the Gemological Institute of America (GIA). Below: how one step shows, what gold does, and what fluorescence means.

At a glance

- G has slightly less colour than H, and both sit in GIA's near colourless group. No source we found measures how often people can see the step.
- Colour is graded loose and table down, so a set diamond looks different.
- GIA says white metal suits colourless and near colourless stones, and a yellow gold band accentuates yellow at M and lower.
- GIA puts fluorescence at about a quarter to a third of the diamonds it examines and treats it as an identifying feature, not one of the 4Cs.

## Diamond colour grade chart: the D to Z scale in one table

GIA grades colour from D, colourless, to Z, light, and it [introduced this scale in 1953](https://4cs.gia.edu/en-us/diamond-color/). Five bands group the letters, with what GIA says an untrained eye can see.

| Letters and GIA label | What GIA says about seeing it |
| --- | --- |
| D to F: Colourless | An untrained eye cannot tell it from near colourless. |
| G to J: Near colourless | Colour is often unseen except by trained graders. |
| K to M: Faint | Still difficult to see with an untrained eye. |
| N to R: Very light | Can be seen in larger stones. |
| S to Z: Light | Can be seen in stones of many sizes. |

The International Gemological Institute (IGI) also grades D to Z, but its labels below J differ between its own pages, so we print GIA's. Our [certificates guide](https://mazimo.ae/journal/diamond-certificates-igi-gia-dubai) compares the two laboratories.

## How diamond colour grade is measured: table down, against master stones

GIA grades colour with the stone loose, table down, under controlled lighting, by comparing it with master stones: reference diamonds of known grade, one per letter. [GIA's 2008 method paper](https://www.gia.edu/doc/Coloring-Grading-D-to-Z-Diamonds-at-the-GIA-Laboratory.pdf) has the grader look through the pavilion, the pointed lower half, from about 12 to 15 inches (30.5 to 38 cm) away, without magnification.

The same paper sets daylight-type lamps of 5500 to 6500 K with a colour rendering index of 90 or above. A letter is a range, not a point. GIA's master stones sit at the least coloured end of each range, so a stone with more colour than the G master but less than the H master is graded G. So a stone at the more coloured end of G and one at the least coloured end of H can sit closer together than two G stones at opposite ends of the range. That inference is ours.

[IGI's method](https://www.igi.org/diamond-grading-process/) differs: the stone is upside down, viewed through the side, and graders reach a consensus. In a ring it is seen face up. Our [4Cs guide](https://mazimo.ae/journal/diamond-4cs-guide) puts it simply: one grade apart is hard to see once set.

## G vs H diamond colour grade: can you see the difference?

G has slightly less colour than H, and one step is small. [GIA's buying guide](https://4cs.gia.edu/en-us/blog/how-to-buy-a-quality-diamond/) says many people cannot tell that diamonds down to the G to H range have colour. The same guide says most people cannot see colour down to G unless they compare the stone side by side with one of much higher colour grade.

GIA's 2008 paper finds that untrained observers often see no difference between two or three adjacent master stones, and calls whole-grade differences extremely subtle. IGI says colour at G is [often undetectable once mounted](https://www.igi.org/consumer-education/diamond-4cs/diamond-color/). No source we found measures G against H directly: only a side by side look at the actual stones, in your chosen metal, answers it for your eyes.

Size changes the answer. Our advice is that colour shows more in bigger stones, at the tips of elongated shapes and in step cuts, as our [guide to diamond shapes](https://mazimo.ae/journal/diamond-shapes-guide) explains. GIA's buying guide says to consider a higher colour grade for a step cut or a stone with one or two tips. Length matters too: the [Oval Solitaire Ring, 3.5 ct](https://mazimo.ae/product/oval-solitaire-ring-3-06-ct), has a centre of about 12.03 × 8.12 mm, a ratio of about 1.48 (12.03 ÷ 8.12), against about 8.03 mm across for the [Round Six Claw Solitaire Ring](https://mazimo.ae/product/round-six-claw-solitaire-ring). (The ring pages round these to 12 × 8.1 mm and 8 × 8 mm.)

## Which diamond colour suits white, yellow and rose gold

The metal changes how a diamond's colour reads, not the grade on its report. [GIA explains](https://4cs.gia.edu/en-us/blog/engagement-ring-setting-metals/) that facets act like tiny mirrors reflecting their surroundings, including the band. Its advice by band:

| Colour band | What GIA says about the setting |
| --- | --- |
| D to F | A white metal setting is the ideal choice. |
| G to J | Good candidates for a white metal setting. |
| K and L | A middle zone: yellow gold or white metal, by the effect you want. |
| M and lower | A yellow gold band accentuates the yellow. |

GIA adds that yellow gold prongs could lend some yellow to a colourless stone. Its buying guide says a warm stone set in yellow or rose gold can help disguise its colour.

We suggest G or H for white gold and H to J for yellow or rose: advice, not a GIA rule, though GIA's buying guide also advises G to H or higher for white gold. Our [yellow, white and rose gold guide](https://mazimo.ae/journal/yellow-white-rose-gold-engagement-ring) covers the metals.

Every Mazimo ring comes in 18K white, yellow or rose gold with the same stones. White gold is the default and is rhodium plated: see [rhodium plating and care](https://mazimo.ae/journal/white-gold-rhodium-plating-care-uae). Below, the Oval Solitaire Ring, 3.5 ct, is shown in [white](https://mazimo.ae/product/oval-solitaire-ring-3-06-ct), [yellow](https://mazimo.ae/product/oval-solitaire-ring-3-06-ct?metal=yellow) and [rose](https://mazimo.ae/product/oval-solitaire-ring-3-06-ct?metal=rose) gold. These are renders: they show the metal, not a stone's colour grade.

[Oval Solitaire Ring, 3.5 ct, Oval · 18K white gold](https://mazimo.ae/product/oval-solitaire-ring-3-06-ct) [Oval Solitaire Ring, 3.5 ct, Oval · 18K yellow gold](https://mazimo.ae/product/oval-solitaire-ring-3-06-ct) [Oval Solitaire Ring, 3.5 ct, Oval · 18K rose gold](https://mazimo.ae/product/oval-solitaire-ring-3-06-ct)

## Diamond fluorescence: what the report line means

Fluorescence is the visible glow some diamonds give off under ultraviolet (UV) light, and GIA reports its strength as None, Faint, Medium, Strong or Very Strong under long-wave UV. GIA [considers it an identifying characteristic](https://4cs.gia.edu/en-us/blog/fact-checking-diamond-fluorescence-myths-dispelled/), not one of the 4Cs. None covers a range from indiscernible to very faint.

[GIA's 2012 figures](https://4cs.gia.edu/en-us/blog/understanding-diamond-fluorescence/), restated in [2023](https://4cs.gia.edu/en-us/blog/diamond-fluorescence-good-bad/), put fluorescence at 25 to 35% of the diamonds it examines: about a quarter to a third. An [IGI article of July 2023](https://www.igi.org/diamond-fluorescence-the-bad-and-the-beautiful/) gives 35 to 50% for natural diamonds.

The hazy case is rare. GIA says fewer than 0.2% of the fluorescent diamonds it received looked hazy or oily: fewer than 1 in 500 (0.2 ÷ 100 = 1 ÷ 500).

In [a 2018 GIA study](https://4cs.gia.edu/en-us/blog/fact-checking-diamond-fluorescence-myths-dispelled/), observers could not consistently discriminate fluorescence-related effects in jewellery-buying conditions. [The 2023 page](https://4cs.gia.edu/en-us/blog/diamond-fluorescence-good-bad/) says bluish fluorescence can make a faint yellowish stone look more colourless in natural daylight, and the report grade is unchanged. GIA calls fluorescence neither good nor bad, and notes that jewellery professionals disagree about it.

## Do lab grown diamonds have fluorescence?

[GIA says](https://www.gia.edu/hpht-and-cvd-diamond-growth-processes) lab grown fluorescence is often stronger under short-wave than long-wave ultraviolet light, the opposite of natural diamonds that fluoresce, and a particular stone may show none. Steven Rees, executive director of [IGI's North America laboratory, said in July 2023](https://www.igi.org/diamond-fluorescence-the-bad-and-the-beautiful/) that about 10% or less of lab grown stones show it: one laboratory's experience.

[One public IGI sample report](https://pdf.igi.org/FDR723533046.pdf) for a lab grown stone, dated July 2025, prints Color D and Fluorescence NONE. Since [1 October 2025](https://www.gia.edu/gia-news-press/updated-laboratory-grown-diamond-services-to-launch-october-1), GIA has sorted loose lab grown stones of 0.15 ct and up into Premium or Standard on colour, clarity, polish, symmetry and, for rounds, cut together. Premium needs colour D plus tighter clarity and finish limits; Standard covers colour E to J. GIA's chart lists no fluorescence criterion. See also [lab grown pros and cons](https://mazimo.ae/journal/lab-grown-diamond-pros-and-cons) and [lab grown against natural in the UAE](https://mazimo.ae/journal/lab-grown-vs-natural-diamonds-uae).

## Colour wording traps on quotes and reports

- **A letter without a laboratory.** GIA and IGI use different methods, so name the laboratory beside the letter.
- **A letter without the fluorescence line.** Ask for both.
- **Near colourless for any letter.** GIA uses it for G to J only.
- **The asterisk.** On a [GIA natural diamond report](https://www.gia.edu/dam/jcr:2fb6ec66-085c-4106-9b7f-11ffc27b0438/8.5x11%20How%20to%20Read%20a%20Diamond%20Grading%20Report%202026.pdf), an asterisk beside the colour grade means a colour treatment was detected.
- **Blue white.** In the United States, the Federal Trade Commission (FTC) [treats](https://www.ecfr.gov/current/title-16/chapter-I/subchapter-B/part-23/section-23.15) it as deceptive for a diamond showing any colour other than blue or bluish in north daylight. That is US guidance only, and we found no UAE rule.

## What to ask when comparing two diamond quotes

Two quotes are comparable only when the letter, laboratory, fluorescence line and metal match. Ask whether the letter is for the centre stone only.

A grading report accompanies the centre diamond where applicable, and the gold has its own Mazimo certificate of purity. Our ring pages state no colour or fluorescence grade. When you ask for a price, ask which letter, fluorescence line and laboratory it is for, and compare the answers. See also [eye-clean clarity](https://mazimo.ae/journal/eye-clean-diamond-vs1-vs2-si1) and [cut grade](https://mazimo.ae/journal/diamond-cut-grade-excellent-vs-ideal).

## When the colour letter is not enough

A letter cannot rank two stones on its own. It says nothing about cut, and our [4Cs guide](https://mazimo.ae/journal/diamond-4cs-guide) says a well cut H looks livelier than a poorly cut E. It does not apply to fancy colours: a stone with more colour than the Z master, or a colour other than yellow, brown or grey, sits outside the scale. And it cannot tell you how a set stone looks on your hand.

## Rings in white, yellow and rose gold at Mazimo, Dubai

Every ring is made to order, in UAE sizes 46 to 62, with a natural or lab grown centre diamond. You can [book a viewing](https://mazimo.ae/appointment) in Deira and try rings on with one of our directors. In our designer, the same 1.50 ct oval solitaire, about 8.8 × 6.5 mm, opens in [white gold](https://mazimo.ae/design#style=solitaire&shape=oval&ct=1.50&metal=white&dia=lab), [yellow gold](https://mazimo.ae/design#style=solitaire&shape=oval&ct=1.50&metal=yellow&dia=lab) and [rose gold](https://mazimo.ae/design#style=solitaire&shape=oval&ct=1.50&metal=rose&dia=lab). The Oval Cluster Ring and the Round Six Claw Solitaire Ring are shown below.

[Oval Cluster Ring, Oval · 2 ct](https://mazimo.ae/product/oval-cluster-ring) [Round Six Claw Solitaire Ring, Round · 2 ct](https://mazimo.ae/product/round-six-claw-solitaire-ring)

We last checked these GIA and IGI pages on 17 October 2026.

## Questions people ask

### Is G or H colour better, and can you see the difference?

G has slightly less colour than H. GIA says many people cannot tell that stones down to G to H have colour, and our view is that one grade apart is hard to see once set. We found no study comparing G with H, so view the actual stones.

### Which diamond colour suits yellow gold?

GIA says a warm stone set in yellow or rose gold can help disguise its colour, while a yellow gold band accentuates the yellow at M and lower. Yellow gold prongs could lend yellow even to a colourless stone. We suggest H to J in yellow or rose: our advice, not GIA's.

### Is fluorescence bad, and does it make a diamond look cloudy?

GIA says it is neither good nor bad, and advises viewing the stone in different lighting, including daylight. Not by itself, says [GIA's 2023 page](https://4cs.gia.edu/en-us/blog/diamond-fluorescence-good-bad/): haze comes from light-scattering features.

### What does faint fluorescence mean on a diamond report?

Faint is the step above None on GIA's scale. With faint to medium fluorescence, GIA says you are unlikely to notice it in most lighting.

### Can lab grown diamonds have fluorescence?

Yes. GIA says it is often stronger under short-wave than long-wave UV, and a particular stone may show none.

**At Mazimo.** Design your ring in the [ring designer](https://mazimo.ae/design), then message us on WhatsApp for the price, or visit Al Manal Center, Deira, minutes from the Gold Souk. Each ring is 18K, hallmarked in Dubai and delivered insured across the UAE at no charge.

Prices and rates mentioned are indicative at the time of writing. For today's number see [today's gold rate](https://mazimo.ae/gold-rates), or [message the boutique](https://mazimo.ae/contact).