Basics 6. Colour: RGB, RGBW, colour wheels and CMY

Colour is the first thing an audience notices and the first thing a beginner runs into: you dial in a beautiful turquoise in the software and the fixture produces something murky green. Or two seemingly identical fixtures on identical values glow in different shades. None of this is a fault — it is simply how fixtures make colour. Let’s sort it out, and understand along the way why white is the most temperamental colour of all.

Light adds up, it does not blend

The first thing to rewire in your head: light does not behave like paint. Mixing paint subtracts — the more colours, the darker and muddier. Mixing light adds — the more colours, the brighter and lighter.

This is called additive mixing. The three primaries are red, green and blue:

What you add	What you get
Red + Green	Yellow
Green + Blue	Cyan
Red + Blue	Magenta
Red + Green + Blue	White

Fig. 1 — Additive mixing: three circles of light and the colours where they overlap

That is exactly how the vast majority of modern fixtures work: three colours of LED inside, and you set the brightness of each on its own channel. Such fixtures are called RGB or «3-in-1» — three chips in one housing.

💡 Tip: when you are after a particular shade, do not think «how much blue do I add» but «which of the three lamps are lit and how brightly». Orange is bright red plus about a third of green. Pink is bright red plus a touch of blue. Two minutes of experimenting on a real fixture explains this better than any table.

Why white is the hardest colour

Formally, white is R255 + G255 + B255. In practice it comes out cold, bluish or slightly green: the different LED colours have different brightness and different spectra, and matching them perfectly is hard. On video that white looks even worse — the camera exaggerates the imbalance.

That is why manufacturers add extra chips:

Marking	What is inside	What it gives
RGB (3-in-1)	Red, green, blue	The basic set; mediocre white
RGBW (4-in-1)	+ White	A proper white and pastel shades
RGBWA (5-in-1)	+ Amber	Warm tones, «tungsten-like» light
RGBWA+UV (6-in-1)	+ Ultraviolet	All of the above plus a UV effect

Hence a practical rule: if the fixture has a dedicated white channel, use it rather than the sum of three colours. The light comes out cleaner and the fixture runs cooler.

💡 Tip: warm white (for weddings, banquets, «cosy» light) on an RGBWA fixture is made like this: white at full plus a little amber. On a plain RGB: red at full, green at about half, a touch of blue.

Change brightness with the dimmer, not with colour

A common mistake: to dim a red, the beginner pulls the red channel down. Technically the light gets dimmer — but the shade drifts with it, and on some fixtures flicker appears at low values.

The right way: colour is set by the colour channels, brightness by the Dimmer channel. Then the shade stays exactly the same at any level, and slow fades look tidy.

⚠️ Careful: some cheap fixtures have no master intensity channel at all — dimming is done purely with the colour channels. You can see this in the channel table: if there is no Dimmer, there is no alternative. Such fixtures behave worse on slow fades.

The colour wheel: colour as a list, not a mix

Powerful lamp-based fixtures (spot heads, scanners, older units) have no LEDs; colour is made mechanically, by a wheel of glass filters spinning in front of the lamp. It is controlled by a single channel that works as a list:

Channel value	What is in the beam
0–9	White (open position)
10–19	Red
20–29	Orange
30–39	Blue
…	…
200–255	Continuous wheel rotation, faster with higher values

Fig. 2 — A colour wheel: a set of ready-made filters instead of smooth mixing

Two consequences surprise beginners:

There are no intermediate colours. You pick from a fixed set, usually 7–14 positions. You cannot fade smoothly from red to blue: the wheel simply turns through the filters in between.
There are «split» positions. Set a value between two positions and the wheel stops halfway, putting two colours in the beam at once — half the pool one colour, half the other. An effective trick, though usually unwanted in theatre.

💡 Tip: on wheel-based fixtures look in the channel table not only for Color but also for Color Macro — that second channel often provides ready combinations and rotation modes.

CMY: smooth colour in expensive fixtures

Professional lamp fixtures use a third method — CMY mixing. Three filters are driven into the beam: cyan, magenta and yellow. Each one gradually blocks part of the spectrum. This is subtractive mixing, the «like paint» kind: the more filter you introduce, the darker and more saturated the colour.

How it is set	Result
All filters out (0, 0, 0)	White
Cyan only	Cyan
Cyan + Yellow	Green
Magenta + Yellow	Red
All three at full	Almost black (the beam is blocked)

The upside of CMY is smoothness: transitions are cinematically soft and any shade is available. The downside is cost and lost output: the filters eat some of the light.

Next to CMY in the channel table you will often find CTO and CTB — colour temperature correction filters. CTO warms the white (towards tungsten), CTB cools it (towards daylight). They are used to match different fixtures to each other or to tune the picture for a camera.

Why identical values give different colours

A situation that will definitely happen: two fixtures of different models, both set to «blue», glowing differently. The reasons are simple:

Different LEDs. Spectra differ between batches and manufacturers — most noticeably on blue and green.
Different chip sets. RGB and RGBW give different whites and different pastels.
Different dimming curves. A value of 128 is half brightness on one fixture and noticeably more or less on another.
Mechanics versus LEDs. A colour-wheel fixture will never match an RGB wash exactly.

What to do about it in practice:

Match by eye, not by numbers. Put the fixtures side by side, call up the colour and nudge the values of the one that stands out.
Do not chase an exact match between different classes of fixture. It is often better to give them different roles: one colour for the wash, another for the beams.
Check on camera if the event is being filmed. Saturated blue and deep red come out worse on camera than to the eye; sometimes it is worth easing off the saturation.

💡 Tip: save the colours that work as presets. Once you have dialled in «warm amber for the first dance», you take it in one click instead of pushing three sliders every time.

📍 How this looks in SvetoMaster: you pick colour with the mouse — from a palette or a colour wheel — and the program distributes it across the channels of the particular fixture: three channels on an RGB wash, the nearest available filter on a wheel fixture, three filters on a CMY unit. Shades you like are stored as colour presets and applied to any set of fixtures, and live mode has quick-colour buttons to repaint the whole room with a single press.

Key points

Light mixes additively: the more colours, the brighter; R+G = yellow, R+G+B = white.
Fixtures come as RGB, RGBW, RGBWA, RGBWA+UV — the extra chips exist above all for a decent white.
Change brightness with the Dimmer channel, not the colour channels.
A colour wheel is a fixed list of filters: no intermediate shades, but split positions and rotation are available.
CMY is smooth subtractive mixing in expensive fixtures; CTO/CTB correct the white’s temperature.
Identical values give different shades on different fixtures — match by eye, and save the good colours as presets.

Coming next: the following lesson is about moving heads: what pan and tilt are, why a head sometimes «drifts», what gobos and prisms do, and what zoom, focus, iris and frost are for.

Next lessonThe moving head: pan, tilt, gobo, prism, zoom