It sounds like a trick question from a primary school quiz. Are black and white colours? The honest answer is that it depends on whether you are talking about light or about paint, and on how strictly you define “colour”. Here is the short version, and then why.
| In light (screens, torches, the sun) | In paint, ink and pigment | |
|---|---|---|
| White | All the colours of light combined | A pigment that reflects all colours |
| Black | No light at all | A pigment that absorbs almost all colours |
| Are they colours? | Not in the strict physics sense | Yes, in everyday and artistic terms |
What colour actually is
To a physicist, colour is a property of light. Light travels as waves, and our eyes can detect waves with lengths from roughly 380 to 750 nanometres (billionths of a metre). Different wavelengths look like different colours: the shortest look violet, then come blue, green, yellow and orange, and the longest look red. That band is the visible spectrum, the same range of colours you see in a rainbow, as I explain in what is a rainbow?
Notice what is missing from that list: white and black. Neither has its own wavelength. So in the strictest physics sense, they are not colours of the spectrum at all.
White: every colour at once
White light is what you get when all the wavelengths of visible light arrive together. Sunlight looks white, but pass it through a prism, or through raindrops, and it splits into the whole rainbow. So in light, white is not the absence of colour but the presence of all of it. You can see this on a screen: every pixel is made of tiny red, green and blue lights, and when all three shine at full strength, you see white. This is called additive colour mixing, because each light you add makes the result brighter.
Black: no light at all
Black is the opposite: it is what you see when little or no light reaches your eyes. Turn the lights off in a windowless room and everything looks black, not because the objects have changed, but because there is no light for them to reflect. In physics terms, black is the absence of visible light, so it is not a colour of the spectrum either.
In paint, it flips
Here is where the confusion comes from. Paint, ink and dye do not make light; they absorb some colours and reflect the rest. A red tomato looks red because its skin absorbs most colours of light and reflects mainly red. White paint reflects nearly all the light that hits it, and black paint absorbs nearly all of it. Mixing paints works the opposite way to mixing light: each pigment you add absorbs more colours, so the result gets darker. This is called subtractive colour mixing, and it is why mixing lots of paints together tends to give you a muddy dark brown or black, never white.
It is also why printers use cyan, magenta and yellow ink, plus black, rather than the red, green and blue of a screen. So to an artist, a printer or anyone choosing paint at the hardware store, black and white are very much colours you can buy in a tin.
What about grey and pink?
Grey sits in between black and white: a grey surface reflects a little of every colour of light equally, so it looks like a dimmer white rather than a colour of its own. Black and white are not the only everyday colours missing from the rainbow, either. Pink and magenta are not on the spectrum. Your brain creates them when your eyes pick up a mix of red and blue-violet light, the two ends of the rainbow, with little green in between. So colour is partly physics and partly the way our eyes and brain interpret what reaches them. If you count only the wavelengths in the spectrum, black, white and pink are all outsiders. If you count everything our eyes can see, they all belong.
The blackest black
If black is all about absorbing light, how black can something get? In 2014, the British company Surrey NanoSystems unveiled Vantablack, a coating made of tiny carbon nanotubes standing on end like a microscopic forest. Light that enters bounces between the tubes until it is absorbed, and the coating swallows up to 99.965% of visible light, according to Wikipedia. It is so dark that a crumpled sheet of foil coated in it looks completely flat, because your eyes have almost no reflected light to pick out the creases.
It also started an art world feud. The company gave sculptor Anish Kapoor exclusive rights to use Vantablack in art, which annoyed many other artists. One of them, Stuart Semple, responded by making his own pigments, including the “pinkest pink”, and selling them to anyone in the world except Kapoor, as the Harvard Art Museums recount. Since then, even darker materials have been made: in 2019, a team at MIT made a material absorbing 99.995% of light, using it to make a 16.78-carat yellow diamond appear to vanish.
So, are black and white colours?
It depends who you ask. To a physicist talking about light, no: white is every colour mixed together and black is the absence of light, and neither has a place of its own on the spectrum. To an artist, a printer or anyone painting a fence, yes: they are pigments you can mix, buy and argue about. So if someone at a trivia night insists that black is not a colour, they are right about light and wrong about paint, and you can both walk away happy. If you are curious about the colours that are on the spectrum, my posts on what a rainbow is and why the sky is blue explain how sunlight gets split into them.
Sources
- Wikipedia: Vantablack
- Harvard Art Museums: Something you can’t see
- Harvard Gazette: Blackest black (2016)
