Coloured noise is steady background sound named after the colours of light, with each colour having a different balance of energy across high and low pitches. White, pink, and brown are the best known, differing in how their energy is distributed across the frequency range. This guide maps the colours and where each is used.
What is coloured noise?
If you have ever played steady static, a fan, or soft rainfall in the background to help you settle, you have already used coloured noise without naming it. Coloured noise (also spelled colored noise) is the umbrella term for steady, random background sound sorted by how its energy is spread across high and low pitches. The colours come from a borrowing from light: just as white light contains every colour mixed evenly, white noise contains every audible pitch mixed evenly, and the other "colours" of noise are named by analogy to describe how the mix is weighted toward the deep end or the bright end.
To follow the rest of this guide, two plain definitions help. A frequency is how fast a sound vibrates, measured in hertz (Hz); low frequencies are deep, rumbling tones and high frequencies are bright, hissy ones. The frequency range (or frequency spectrum) is simply the full span of pitches a sound contains, from the deepest to the brightest. The colour of a noise describes how its energy is balanced across that range. White noise spreads energy evenly; pink noise leans toward the deeper end; brown noise leans deeper still. That balance is the whole idea, and it is why two noises can both be "random hiss" yet sound completely different, one bright and sharp, another soft and rumbling.
One thing worth saying plainly at the outset: coloured noise mostly works by covering up other sounds, a job called masking. A constant, even wash of sound blurs the sudden noises (a slamming door, a passing car, a snoring partner) that would otherwise grab your attention or wake you. That is the honest, ordinary reason people find these sounds useful. Some colours feel more soothing than others, and personal taste matters a great deal, but none of them does anything mysterious to your brain. This page is the map: it defines coloured noise, explains how the colours are set apart, compares them, and points you to the deeper guides for the specific colour or use you care about.
How the noise colours are defined
The colours are not a marketing invention; they come from a real, measurable property used in acoustics and signal processing. That property is power spectral density, which is just a technical way of saying "how much energy a sound carries at each pitch across its range". If you measured a noise and plotted its energy against pitch, the shape of that line is its spectral signature, and the colour names describe the shape of the line.
Start with the reference point. White noise is defined by the Acoustical Society of America as noise whose energy is essentially independent of frequency across a stated range, meaning it carries roughly the same energy at every pitch.1 That flat, even spread is why white noise sounds like a bright, full hiss, similar to untuned-radio or television static. It is the acoustic equivalent of white light, every pitch present in equal measure.
The other colours are defined by how they tilt away from that flat line. Pink noise is defined as noise whose energy varies as the inverse of frequency, often written as 1/f, so its energy falls steadily as the pitch rises.2 In practical terms it drops by about 3 decibels per octave (a decibel is the standard unit for loudness, and an octave is a doubling of pitch), which is why pink noise sounds softer, deeper, and less harsh than white noise, more like steady rainfall than static. Brown noise (also called Brownian or red noise) tilts further still, with energy falling about 6 decibels per octave, giving a deep, low rumble closer to distant thunder or a strong wind.3 The reverse-tilted colours exist too: blue noise rises toward the bright end and violet noise rises more steeply, so both sound thin and hissy, the opposite of brown.3 In short, the deeper the tilt toward low pitches, the softer and more rumbling the noise; the more it tilts toward high pitches, the sharper and hissier it sounds. That single idea, the tilt of energy across the frequency range, is all you need to tell the colours apart.
The main noise colours at a glance
The table below maps the better-known colours by their spectral tilt (which way their energy leans across the frequency range), how they tend to sound, and where people commonly reach for them. It is an overview of the whole family; the per-colour summaries that follow, and the dedicated deep-dive guides they link to, go into each one properly. Treat "typical use" as what people popularly try, not as a proven effect; the evidence question is handled honestly further down.
| Colour | Spectral tilt (energy across the range) | How it sounds | Commonly used for |
|---|---|---|---|
| White | Flat: equal energy at every pitch1 | Bright, full hiss (like static) | Masking sudden noises; background cover |
| Pink | Falls about 3 dB per octave (1/f)2 | Softer, deeper, like steady rain | Relaxation; a gentler masking sound |
| Brown (Brownian, red) | Falls about 6 dB per octave (1/f squared)3 | Deep, low rumble (like distant thunder) | Calm; deep background for focus or sleep |
| Grey | Shaped to sound equally loud across pitches3 | Balanced to the ear, neither bright nor deep | Audio testing; balanced background |
| Green | Loosely, mid-weighted; like natural ambience3 | Mid-range, nature-like wash | Relaxation; "outdoors" feel |
| Blue | Rises about 3 dB per octave toward high pitches3 | Thin, sharp hiss | Audio engineering (dithering) |
| Violet (purple) | Rises about 6 dB per octave, steeper than blue3 | Very thin, brittle hiss | Niche audio uses; tinnitus research tools |
| Black | Mostly silence with occasional energy3 | Near-quiet | Informal label; little practical use |
White, pink, and brown are the three you will actually meet in apps and sleep machines, which is why each gets its own summary and deep-dive guide below. The rest are mostly technical or niche, covered briefly further on.
White noise: the short version
White is the reference colour: an even spread of energy across every pitch, which gives it that bright, full hiss like static.1 Because it covers the whole frequency range evenly, it is good at masking a wide variety of intrusive sounds, which is why white-noise machines and apps are so common for sleep, offices, and nurseries. The honest caveat is that the research on steady noise as a sleep aid is weak, a point covered in the evidence section below, so think of it as "popular and worth trying if you like it" rather than proven. Some people also find the brightness a little harsh and prefer a softer, deeper colour. This is a summary only; for the full picture of what white noise is, where it helps, and what the studies actually show, read the deep dive: our complete guide to white noise (publishes when that cluster ships).
Pink noise: the short version
Pink noise has the same random quality as white but with its energy tilted toward the deeper end, falling about 3 decibels per octave, which makes it softer and less harsh, more like steady rainfall than static.2 Many people find that gentler balance more soothing for relaxing or drifting off, and pink noise is the colour most often studied in sleep research, including some intriguing laboratory work on deep sleep that we describe honestly in the evidence section. As with all these colours, it works mainly by masking, and the everyday evidence for it as a sleep aid is modest, so personal preference is a fair guide. This is a summary only; for what pink noise is and what the research really supports, read the deep dive: our complete guide to pink noise (publishes when that cluster ships).
Brown noise: the short version
Brown noise (also called Brownian or red noise) tilts deeper still than pink, with energy falling about 6 decibels per octave, producing a low, full rumble closer to distant thunder, heavy rain, or a strong wind.3 It has become popular for calm, sleep, and background focus, and a common search is whether brown noise is "good for you". The honest answer is that it is low-risk to try at a sensible volume and many people find its deep, even rumble genuinely relaxing, but there is no strong evidence that it does anything special beyond masking, and the claims that it sharply boosts focus or quiets a busy mind run well ahead of the science. Enjoy it if you like it; do not expect a miracle. This is a summary only; for the detail, including the "is brown noise good for you" question in full, read the deep dive: our complete guide to brown noise (publishes when that cluster ships).
Green, blue, and the rarer colours
Beyond the famous three, a handful of rarer colours fill out the family, and the pillar owns the plain overview of them so you can place each one. Green noise is the least formally defined of the set; it is loosely treated as a mid-weighted noise meant to evoke the ambience of the outdoors, with its energy concentrated in the middle of the range rather than the bright or deep extremes.3 People often ask whether green noise is just white noise with a nicer name; the fair answer is that it is a softer, more mid-range relative, closer in spirit to pink than to white, and there is no rigorous evidence singling it out as uniquely effective. Blue and violet (purple) noise sit at the opposite end from brown: their energy rises toward the high pitches, blue gently and violet more steeply, so both sound thin and hissy.3 They are mostly tools of audio engineering and research rather than relaxation sounds. Grey noise is shaped so it sounds about equally loud at every pitch to a typical human ear, which makes it useful for balanced audio testing.3 Black noise is the loosest label of all, used informally for near-silence with only occasional bursts of energy. If a colour beyond white, pink, and brown catches your interest for sleep or focus, the practical advice is the same as for the big three: try it gently and let your own ear decide, because the evidence does not crown a winner.
Which colour for sleep or focus: a quick summary
The most common question is which colour to pick for sleep or for concentration, and the honest headline is that there is no single proven answer, only sensible starting points and a lot of personal variation. For sleep, the soft, deep colours (pink and brown) are what most people gravitate toward because they feel gentler than bright white noise, but the underlying evidence for any steady noise as a sleep aid is weak, as the evidence section explains. For focus, some people like a deep, even background such as brown noise to blur a distracting room, while others find any noise unhelpful; here too the picture is mixed and individual. The single most reliable rule is to pick whatever you find pleasant and unobtrusive at a low volume, give it a few sessions, and switch if it does not help. This is a deliberately brief, claim-free pointer; for the proper comparisons, see which noise colour suits sleep and which noise colour suits focus (each publishes when that cluster ships), and for the wider context read our overviews of sound for sleep and sound for focus.
Comparing the colours (white against brown, and the other matchups): a quick summary
Once you know the colours exist, the natural next question is how they stack up against each other, and the most-asked matchup pits the bright reference colour against the deep rumble: an even, full hiss versus a low, soft rumble. The plain difference is the tilt we have already met, one spreads energy evenly while the other concentrates it at the deep end, so one sounds sharp and the other sounds soft. Which you prefer is largely a matter of taste and of what you are trying to mask, and neither is proven to beat the other for sleep or focus. The same logic applies to every pairing of colours: they differ in how bright or deep they sound, not in any magic effect. This is a summary only; for the side-by-side comparison in full, read the deep dive: our white and brown noise comparison (publishes when that cluster ships).
What the research says about noise colours
It is worth pulling the evidence together honestly, because coloured noise is an area where confident marketing runs well ahead of careful science. The fair one-line summary is this: the spectral definitions of the colours are solid physics, but the claims that a particular colour reliably improves sleep or focus are, for the most part, weakly supported or untested. Holding both of those at once is the honest read.
The spectral side is the secure part. The definitions of white and pink noise come from formal acoustics standards,12 and the spectral tilts of the other colours are well established in signal processing.3 What a noise colour is, physically, is not in dispute. The contested part is what any of it does for you.
The clearest cautionary evidence concerns white noise for sleep. Despite how widely white-noise machines and apps are recommended, a systematic review in Sleep Medicine Reviews that pulled together the studies on continuous noise as a sleep aid found that the overall quality of the evidence was very low, and that continuous noise could either improve or disrupt sleep depending on the study; the authors concluded that more rigorous research is needed before it is promoted as a sleep aid, and even flagged possible downsides for sleep and hearing.4 That does not mean noise colours cannot help you; plenty of people find them useful. It means the honest status is "popular and possibly helpful, but not well proven", which is very different from how these sounds are usually sold.
The most intriguing research is also the most specialised, and it is important not to confuse it with everyday listening. Scientists have explored whether brief, very quiet pulses of sound, timed precisely to the brain's own slow waves during deep sleep, can deepen that sleep. A 2017 study in Frontiers in Human Neuroscience delivered carefully timed pink-noise pulses to a small group of older adults during deep sleep and reported enhanced slow-wave activity and a related improvement in memory, though with only thirteen participants it is an early, small finding.5 The crucial caveat for a reader is that this works by reading your brain waves in real time and firing sound at the exact right instant, which is a laboratory technique, not what a normal app or a plain "pink noise" track delivers. It is a genuine and exciting research direction, but it is not something you can buy and use at home, and any product implying it has bottled this effect is overclaiming. Sound and the brain remain a serious but still under-studied field; an NIH and Kennedy Center expert workshop, co-authored by senior figures at the National Institutes of Health, was convened precisely to set a research agenda for it.6 The wider point is the same one national health bodies make about sound and wellbeing generally: music-based and sound-based approaches show genuine promise for things like relaxation and sleep, but many of the studies are small and more rigorous work is needed before strong claims are warranted.7 You can see the full citation list behind Sonora's claims on Sonora's evidence base. The calibrated takeaway is steadying rather than dismissive: the colours are real and measurable, some people genuinely find one or another soothing, and masking is a real benefit, but no colour is a proven fix for sleep or focus, so let preference, not hype, lead.
How to use coloured noise (and how Sonora delivers it)
Putting this into practice is simpler than the physics makes it sound. First, pick by ear rather than by reputation: play white, pink, and brown for a minute each and notice which feels most comfortable, because personal preference is as reliable a guide as any here, given that the evidence is mixed. Second, keep the volume low; the goal is a soft, even blanket of sound that blurs sudden noises, not a wall of it, and gentle is just as effective as loud while being far kinder to your hearing. The World Health Organization advises that listening at around 80 decibels is safe for up to about 40 hours a week, with the safe duration falling sharply as the volume rises,8 and it estimates that more than a billion young people are at risk of avoidable hearing loss from unsafe listening, so this matters even for a background sound.9 Third, use a steady, seamless source: an obvious loop or gap can become the very thing your attention latches onto.
This is also where Sonora's approach differs from handing you a single fixed track. Because people respond so differently to the same sound, a one-size-fits-all colour is a blunt instrument; Sonora's premise is to match sound to the listener and the moment, and to be honest about what the evidence supports rather than overpromising. You can Try Sonora free to hear how that adaptive approach feels. Coloured noise is one branch of a wider family of sound-based approaches, each with its own dedicated guide in this Learn library: see our evidence-based overviews of sound healing and the evidence behind it, how binaural beats work, AI-driven adaptive soundscapes, so-called healing frequencies, sound for sleep, and sound for focus. You can also read about our editorial process on the Sonora team page.
