Gemstone colour grading by lab: why one report says vivid, another intense
How AIGS, GRS, Lotus, Bellerophon, GUILD, Gübelin, SSEF, GIA and AGL describe ruby and sapphire colour, why their terms don't line up, and how to compare reports.
There is no shared colour scale for rubies and sapphires. Each laboratory that describes colour uses its own words, steps and reference stones, and some major labs, GIA among them, do not grade coloured-stone colour at all. So when one report says "vivid" and another "intense" or "strong saturation" for a similar-looking stone, the words are sitting at different points on different scales.
AIGS: reference colours rather than a published scale
The Bangkok laboratory AIGS publishes a gallery of "special colour" names for corundum, among them Pigeon Blood, Royal Blue, Cornflower, Padparadscha, Sakura Pink and Golden Canary, plus a chart titled "Ruby & Sapphire Master Stones". AIGS notes that professional assessment relies on its official reference standards, not these images. Colour also feeds the Star Rating on its Master Gemstone Report, with clarity, cutting and weight. Its website shows no named saturation or tone scale for ruby or sapphire.
GRS: what do "intense", "vivid" and "deep" mean?
In its 2015 explanation, GRS (GemResearch Swisslab) set out a five-step scale for red: pinkish red, red, intense red, vivid red and deep red, with vivid at step four. It said it grades in daylight against two master sets, one Burmese and one Mozambican, kept at each of its laboratories. In November 2017 it added two in-between grades, "intense to vivid" and "vivid to deep".
The trademarked "GRS-type" label sits on top of the grade. Rubies graded intense-to-vivid, vivid or vivid-to-deep red can be called GRS-type "pigeon blood", and the equivalent blues GRS-type "royal blue", unless excluded by factors such as beryllium treatment, lead-glass filling, or dominant colour zoning and windowing. On a GRS report, then, "intense" is a step below "vivid", not a synonym. The names themselves are covered in our guides to pigeon blood ruby by lab and royal blue sapphire by lab.
Lotus Gemology: hue, tone and saturation
Lotus Gemology in Bangkok works in three dimensions. Its reports place saturation on a five-step scale running from pastel to vivid, and tone on a five-step scale measured from 0% (white) to 100% (black). Where a stone falls within its ranges, the report can add a colour type: for blue sapphire these include Cornflower, Peacock, Velvet, Royal, Indigo and Twilight; for ruby, Pigeon's Blood and Royal Red. For sapphires with a yellow-to-orange component, whose colour can be unstable, reports issued after 15 November 2025 note the result of Lotus's stability test.
Bellerophon Gemlab: a measured colour grade
Bellerophon describes colour by hue, tone and saturation, using 15 basic hue names and about 90 grades in what it calls a level 3 simplified colour system. The grader records one overall face-up colour after comparing the stone side by side with at least two reference gems. Colour is also measured with instruments such as spectrometers and colorimeters, with grades defined in CIELAB coordinates, but Bellerophon says the grader's eye makes the final decision. The lab calls the result a description of the main colour in standardised terms, and notes that a recut can move a stone several grades.
GUILD Gem Laboratories
GUILD says its Standard Report includes colour grading alongside weight and cutting style, and that stones meeting its top benchmarks may receive a commercial name; the GUILD FOLIO adds a fuller breakdown of the colour grade. Its website does not publish the scale, the terms or the reference stones behind those grades.
Gübelin: colour in words, quality in points
Gübelin Gem Lab's published colour material centres on named colour terms rather than a stepped scale. Four terms have published criteria on its website: pigeon blood red, royal blue, padparadscha and crimson red. For the first two, master stones set the permitted ranges of hue, saturation and tone, and Gübelin says it agreed with SSEF in 2015 to harmonise those definitions.
Separately, the Gübelin Gemstone Rating, introduced in 2021, scores eligible stones from 75 to 100 points across quality, rarity and salience; colour (hue, depth, saturation, homogeneity) is part of quality.
SSEF: a description, not a grade
SSEF describes colour as a hue, an optional modifier and a saturation level. For blue sapphire it lists blue of medium, medium strong and strong saturation; for ruby, red of medium strong and strong saturation. Only unmounted stones of strong saturation that meet all its criteria can be called "pigeon blood red" or "royal blue". For those terms SSEF compares the stone with natural master sets in a standardised light box, face-up and tilted 20° in each direction. It also cautions that the report photograph does not necessarily show actual colour.
Does GIA grade the colour of rubies and sapphires?
No. GIA states that it does not grade or give quality analysis for sapphire or other coloured stones, and its FAQ adds that no broadly accepted grading system for them exists. Its identification and origin reports record colour as an identifying characteristic, with a photograph. GIA's announcement of the redesigned reports issued from 1 January 2026 mentions no colour grade; see our note on GIA coloured gemstone reports in 2026. GIA does use masterstones to judge whether red is dominant, the line between ruby and pink sapphire. Its hue, tone and saturation framework, which JCK described in 1998 as 31 hues and six saturation levels up to vivid, belongs to teaching and trade use rather than its reports.
AGL: a numerical colour rating
AGL in New York gives the most explicit grade. Its Prestige Report with grading assigns a Color Rating from 1 to 10 combining hue and saturation, a tone figure from 0% (white) to 100% (black), and both an average grade and the range visible face-up. All stones are judged in a standardised lighting environment. AGL's page does not name its references; JCK reported in 1998 that the lab had developed and used its own Color/Scan system.
Why the same stone reads "vivid" at one lab and "intense" at another
- Different ladders: at GRS, intense sits below vivid; Gübelin uses "intense" inside its top-tier definitions; SSEF's highest saturation word is "strong"; Lotus runs from pastel to vivid; AGL uses numbers.
- Different master stones: each lab calibrates its terms against its own reference sets.
- Different light and geometry: GRS cites daylight, SSEF a light box with a 20° tilt, and Bellerophon specifies colour temperature, illuminance, colour rendering and metamerism. JCK noted that incandescent light makes ruby look redder.
- Human judgement: AIGS chairman Kennedy Ho told JNA in 2026 that colour perception shifts with lighting, environment and the individual gemmologist's eyesight, and called for shared standards.
- Changing scales: GRS's 2017 update means an older report may use fewer steps than a recent one.
A colour word on a lab report only means something on that lab's own scale.
How to compare two certified stones online
- Read each term against its own lab's scale.
- Check the report online and note its date; our guide on how to verify a gemstone lab report explains the steps.
- Look at the modifier and tone, not only saturation: a "purplish" or dark stone can share a saturation word with a purer one.
- Do not judge colour from report photos or screens. Ask for video of both stones in the same daylight-equivalent and warm light.
- Where possible, compare stones graded by the same laboratory, such as two GRS reports or two Lotus reports.
In our rubies and blue sapphires, every stone is offered at a fixed price and listed with its laboratory, report number and treatment status. You can request a quotation or ask a question on WhatsApp from any product page.
This article explains laboratory colour terms only and does not assess value. It is general information, not investment, tax or legal advice.
Frequently asked questions
Is "vivid" on a GRS report the same as "vivid" on a Lotus report?
Not necessarily. GRS uses vivid as step four of a five-step red scale against its own master sets, while Lotus Gemology uses vivid as the top of a five-step saturation scale; the two scales were not built to match.
Which laboratories give a numerical colour grade?
AGL's Prestige grading report gives a Color Rating from 1 to 10 plus a tone percentage. Bellerophon's simplified colour system has about 90 grades, defined in CIELAB coordinates.
Is a colour grade the same as "pigeon blood" or "royal blue"?
No. At GRS, SSEF and Gübelin these trade terms are added only when a stone meets extra criteria, including treatment and quality conditions, on top of the colour description.
Can a stone's colour grade change?
It can. Bellerophon notes that recutting can shift a grade by several steps, and GRS added intermediate grades in 2017, so older and newer reports may use different steps. For sapphires whose colour may be unstable, Lotus reports issued after 15 November 2025 note the result of its stability test.
