Colour Systems and Models

RGB, CMYK, HSL, Lab, OKLCH, Munsell, NCS and the rest: what each was designed for, why they disagree about the same colour, and which to use for which job.

Commercial catalogue systems are described as systems; their proprietary colour data is not reproduced.

12 topics · 41 evidence-labelled claims · 24 sources

Tools

Colour Converter

Device models

RGB, CMYK, HSL and HSV.

How does the RGB colour model work, and why isn't an RGB value a colour on its own?RGB describes a colour as amounts of three coloured lights — red, green and blue — added together, which is how every screen and…How does CMYK work, and why is there no single correct CMYK for a colour?CMYK describes a printed colour by how much cyan, magenta, yellow and black ink to lay on paper.What are HSL and HSV, and why is their 'lightness' misleading?HSL and HSV are rearrangements of RGB into a hue angle plus two other numbers — saturation and lightness, or saturation and value…Which colour system should I use for my task?Use the system whose purpose matches the job: sRGB (HEX, rgb()) or Display P3 to deliver colours to screens; OKLCH to design pale…

CIE and perceptual spaces

XYZ, Lab, LCh, OKLab and OKLCH.

What is CIE XYZ, and what does the horseshoe chromaticity diagram show?CIE XYZ is the 1931 international standard for turning a light's spectrum into three numbers that predict whether two lights will…What is CIELAB, and why is it the standard for measuring colour difference?CIELAB (L*a*b*), defined by the CIE in 1976, converts XYZ into a lightness axis L* and two opponent axes — a* from green to red a…What is OKLab, and how does it improve on CIELAB?OKLab is a perceptual colour space published by Björn Ottosson in December 2020 and OKLCH is its polar form.Why does the same colour get different numbers in every colour system?Because each system measures different things for different purposes.

Colour order systems

Munsell, NCS and catalogue systems.

How does the Munsell colour system work, and why is it still used?Munsell orders surface colours by three visually judged dimensions — hue, value (lightness) and chroma — each divided into steps…What is the Natural Colour System, and how is an NCS code read?NCS describes colours by how they look in relation to six elementary colours that people perceive as pure — white, black, yellow,…What are RAL colours, and how do RAL CLASSIC and the RAL DESIGN SYSTEM differ?RAL colours are standardised, numbered colour references maintained by RAL in Germany, used across Europe for coatings, signage,…What is the Pantone Matching System, and what does a Pantone number actually specify?The Pantone Matching System is a proprietary catalogue of numbered spot colours, each with printed swatches and a formula for mix…