Colour Models & Systems

Every colour model is a way of putting numbers to colour, and they split into two families by a single physical question: are you adding light or subtracting it? Get this distinction and half the confusion around colour models disappears.

Additive colour is the colour of light itself. Start with darkness - a black screen - and add coloured light. The primaries of light are red, green and blue, and they add up: red plus green light makes yellow, all three together make white. This is how every screen you own works. Zoom into a phone display and you find tiny red, green and blue emitters; at arm's length your three cones blend them into a full-colour image. More light means brighter and, eventually, whiter. This is the world of RGB.

Subtractive colour is the colour of surfaces - paint, ink, dye, stained glass. Here you start with white (a lit sheet of paper) and every pigment you add subtracts some wavelengths by absorbing them, leaving less light to reflect. The primaries of pigment are cyan, magenta and yellow, because each one subtracts one of the light primaries. Pile them all on and, in theory, you absorb everything and get black - in practice a muddy brown, which is why printing adds a real black ink, the 'K' in CMYK. More pigment means darker.

This is why the two worlds behave in opposite directions and never perfectly agree. On a screen, mixing moves you toward white and light; in a paint tray, mixing moves you toward black and mud. A colour glowing on your monitor is made of emitted light in the RGB world; the 'same' colour on a wall is made of absorbed light in the subtractive world, and there are vivid screen colours no pigment can hit. Knowing which world you are in - designing a slide (additive) or specifying a paint (subtractive) - tells you how mixing will behave and warns you, early, why the render and the room will never match exactly. Module 9 returns to managing that gap.

RGB and CMYK describe colour the way a machine mixes it - so much red light, so much cyan ink. They are precise and essential, but they are unintuitive for a designer: nobody thinks 'I want a bit less green and more blue' when choosing a wall colour. HSL - hue, saturation, lightness - was built to match how people actually reason about colour, and it maps almost exactly onto the three dimensions from Lesson 0.1.

Hue is the colour family, expressed as an angle from 0 to 360 degrees around a colour wheel: red near 0, green near 120, blue near 240. Saturation is how pure the colour is, from 0 (a neutral grey) to 100 (fully vivid) - this is chroma by another name. Lightness runs from 0 (black) through the vivid colour to 100 (white) - this is value. A close cousin, HSV (or HSB), swaps lightness for 'brightness' and behaves slightly differently, but the intent is the same: separate the which colour from the how strong from the how light, so each can be adjusted on its own.

This separation is the reason HSL is worth knowing even if you never type a colour code. It gives you a mental model for fixing colours. A scheme that feels too loud? Pull the S down and leave H and L alone - the hues stay, the shouting stops. A palette that looks flat and washed out? The L values are probably all bunched in the middle; spread them. A colour that is 'nearly right but a touch cold'? Nudge the H a few degrees warmer. Designers who think in HSL diagnose colour problems as adjustments on three independent dials, exactly as a professional describes them out loud - 'right hue, drop the saturation, take the value down a step' - rather than starting over with a new swatch.

RGB and HSL live inside devices; they tell you nothing you can hand to a painter or a fabricator. For the physical world we need colour-order systems - catalogues that give real, reproducible colours a fixed name or number, so 'this exact colour' can travel from your drawing to a factory in another country without ambiguity. Four matter in architecture and interiors.

Munsell is the great-grandparent and the most rational. It describes any colour in three perceptual steps - Hue, Value and Chroma - written like 5R 4/14 (hue 5R, value 4, chroma 14). Its genius is that equal steps in the notation look like equal visual steps, which makes it the reference for teaching and for describing soils, materials and skin. It is a way of thinking as much as a swatch book.

NCS (Natural Colour System), the Scandinavian standard, notates colour by how much it resembles the elementary colours plus black and white - S 1080-Y90R means 10% blackness, 80% chromaticness, a yellow with 90% red in it. It is widely used in European architecture for facades and interiors because it describes colour the way the eye relates it to pure references.

Pantone (the PMS) is a proprietary library of pre-mixed spot colours, indispensable in branding, graphics and print - Pantone 186 C names one specific red on coated stock. RAL, a European standard originally for paints and coatings, is the workhorse for specifying powder-coated metal, joinery and industrial finishes - RAL 3020 is 'traffic red', RAL 9010 a common white. Each system exists because a particular industry needed unambiguous colour, and each comes with physical fan-decks so you match against a real sample, not a screen.

It is tempting to treat a colour code as a formality - the painter will 'get it about right'. On site, 'about right' is how a scheme quietly falls apart. A colour named in words - 'warm white', 'sage', 'terracotta' - is an invitation to a dozen different results, because those words map to hundreds of real products. A colour named in a proper system - NCS S 2005-Y20R, RAL 7016, Munsell 5Y 8/2 - is a single, checkable target. The difference shows up as rework, delay and argument when it is missing, and as calm certainty when it is there.

Precise notation does three jobs at once. It communicates unambiguously to whoever mixes or makes the colour, across languages and suppliers. It lets you verify the delivered colour against the specified one by comparing to a physical chip under proper light, rather than arguing from memory. And it lets you coordinate colour across trades - the paint, the powder-coated railing, the tile grout, the signage - by pinning each to a nameable target instead of hoping they land in the same family.

In India this discipline matters just as much, and the tools are close at hand. The big paint houses - Asian Paints, Berger, Nerolac, Dulux - each publish their own coded shade cards and can tint to a fan-deck reference, and most will accept or cross-reference an NCS or RAL target for a specified job; powder-coaters and fabricators here work to RAL as a matter of course. So there is no excuse for a colour to leave your drawing as a word: write the brand-and-code, or the NCS/RAL reference, and it becomes a target a supplier in Ludhiana or Coimbatore can hit.

Two honest cautions. First, notation is not a substitute for seeing: always confirm the chosen code against a real sample, at size, under the actual light, because a number on a page still has to survive Lesson 0.2's realities of context and vision. Second, systems do not freely convert - a Pantone spot colour has no exact RGB or CMYK twin, and a screen preview of a RAL number is only an approximation. The skill is to specify in the system that matches the material (RAL or NCS for architectural paint and coatings, Pantone for print and brand, Munsell for description and analysis) and to carry a physical reference for sign-off. We build the full specification workflow in Module 7; here, simply adopt the habit that a colour is not decided until it has a name a stranger could reproduce.