Colour model

A colour model is a system or framework for understanding, organising and working with colour. It can be as simple as remembering the sequence of colours in a rainbow or represent an essential component of industrial and commercial enterprises.

  • A colour model, underpinned by a colour theory, provides a precise and replicable approach to understanding:
    • How the human eye perceives light and interprets colour.
    • Different types of colour such as the colours produced by lights, pigments and inks.
    • How to manage the diverse ways colour is processed by equipment such as cameras, digital screens and printers.
  • Whether or not we recognise it, whenever we are working with colour, we are adopting a colour theory, a colour model and a colour space. For example:
    • Children are taught how to mix acrylic or powder colours together. Early on they discover that red and yellow make orange, and that yellow and blue make green. This is the RYB colour model.
    • Children are taught to recognise the colours of the rainbow. This is the spectral colour model.
    • Anyone who has replaced the inks in a printer knows that they use cyan, magenta and yellow inks. This is the CMY colour model.
    • Whenever we use TVs, computers, and phone screens we are using the RGB colour model.
  • At another level, colour theories and associated colour models are used to establish terms and definitions, rules, conventions and systems of notation for encoding colours and managing their relationship with one another in ways applicable to industrial applications such as cosmetics, food, architecture and packaging.

Colour models enable us to:

  • Make sense of the concept of colour in relation to human vision and the world around us.
  • Use colours in logical, predictable and replicable ways.
  • Understand how to mix a particular colour whether using lights or pigments, inks or dyes.
  • Specify colours using names, codes, notation, equations etc.
  • Organise and use colour for different purposes and in different contexts. Think of fabrics, interiors or vehicles.

Widely used colour models include:

CMY(K) Colour Model
  • CMY (cyan, magenta, yellow) is a subtractive colour model. It is the standard colour model for digital printing. Digital printers usually use a fourth component, black ink (K), to increase the density of darker colours and blacks.
HSB Colour Model
  • HSB (hue, saturation, brightness) is a popular additive colour model. Many people find it more intuitive and so easier to use than RGB, particularly when adjusting colour using digital applications such as Adobe Creative Cloud.
  • HSB is one of a family of colour models that also includes HSV (hue, saturation, value) and HSI (hue, saturation, intensity).
RGB Colour Model
  • RGB (red, green, blue) is an additive colour model and is closely related to the trichromatic theory of colour vision. It is widely used in digital cameras, for producing colour on digital screens and with software such as Adobe Creative Cloud.
RYB Colour Model
  • RYB (red, yellow, blue) is a subtractive colour model. It is the standard colour model used for artist paints and when mixing opaque inks, dyes and pigments.
Spectral Colour Model
  • The spectral colour model is neither an additive nor a subtractive colour model and is concerned instead with understanding the effects of refraction and dispersion on wavelengths of light and the way they separate into rainbow colours.
Trichromatic Colour Model
    • The trichromatic colour model posits that the human eye perceives colour through the stimulation of three types of cone cells in the retina and that each type responds to different wavelengths, corresponding roughly to red, green, and blue.
About why we use colour models
  • Colour models help to relate and coordinated colours with one another when working with different light sources, media such as paints or inks, objects and materials.
  • Colour models clarify the ways in which coloured lights, transparent inks and opaque paints (etc.) all produce different results when mixed.
  • Colours models help us manage the fact that colours behave and appear differently:
    • When emitted by different types of light sources.
    • Depending upon the type of media – inks, dyes, pigments.
    • When seen or used in different situations (indoors, in sunlight, in low light, on a digital display etc.)
    • When applied to, mixed with, or projected onto different materials.
    • When used for different purposes (fabrics, electrical wiring and components, print media, movies etc.)
About additive and subtractive colour models

There are two main types of colour models, additive and subtractive.

Additive Colour Models
  • Additive colour models are used when blending light to produce colour.
  • The primary colours for most additive models are red, green, and blue (RGB).
  • When combined at full intensity, they produce white light.
  • The additive RGB model (and HSB colour model) is central to display technologies such as computer screens, TVs and phone screens.
  • The additive spectral colour model is particularly useful for developing an understanding of the relationship between wavelengths of light within the visible spectrum and corresponding colours.
  • Additive models are based on the way human eyes perceive colour, with each colour being produced by a combination of different wavelengths. In contrast, a subtractive model is based on the way pigments reflect light.
Subtractive Colour Models
  • Subtractive colour models are used when working with pigments, inks and dyes.
  • The primary colours for most subtractive colour models are cyan, magenta, and yellow (CMY).
  • When combined cyan, magenta, and yellow produce black.
  • The subtractive CMY colour model and CMYK colour model are central to printing technologies.
  • In practice, the CMY colours often can’t produce a perfect black when mixed due to impurities in the pigments or inks, so a fourth ‘Key’ component (represented as K) is often used in printing to produce a true black.
About colour theories, models, spaces and management systems

Colour theory, colour models, colour spaces, and colour management systems are integral to understanding, representing, and manipulating colour in various fields.

Colour Theory
  • A colour theory is a set of principles and concepts used to understand how colour works, how colours relate to each other, and how they are perceived or interpreted by the human eye. A colour theory allows us to predict in advance how colour behaves in practice.
Colour Model
  • A colour model is a practical application of colour theory. In both industrial and design contexts a colour model is and mathematical representation or system for creating a full range of colours using a set of primary colours. Examples include the RGB (Red, Green, Blue) model for light-based colours and the CMY (Cyan, Magenta, Yellow) model for pigment-based colours. The choice of a colour model depends on the medium (light, paint, ink, etc.) and the application (canvas, monitor, printer, etc.).
Colour Space
  • A colour space is a specific organization of colours derived from a colour model. It can be used to define a gamut or subset of colours that can then be successfully applied within a particular context or for a specific purpose. Examples of colour spaces used in digital design include sRGB and Adobe RGB within the RGB model, each of which encompasses a different range of colours.
Colour Management System
  • These are systems or protocols designed to ensure consistent and accurate colour reproduction across different devices, media, and lighting conditions. They consider the specifications of the devices used to capture, edit, or display colour, as well as the lighting conditions in which colours are viewed.

In summary, a colour theory provides the underlying concepts, a colour model provides a framework to represent these concepts, a colour space defines a specific range of colours that can be generated within the parameters of the model, and a colour management system ensures consistency and accuracy in reproducing colours across different contexts and devices.