Open any sleep or focus app and you'll find a menu of noises named after colors. White noise. Pink noise. Brown noise. Sometimes green, blue or even violet. Online, people swear by one or another for falling asleep, quieting a busy mind, or getting through a work session in a loud apartment.

The colors aren't marketing inventions. They describe real, measurable differences in how sound energy is spread across frequencies. What the research says about their effects is more modest than the enthusiasm online.

Why sound has colors

Every sound can be described by its frequencies, from low rumbles to high hisses. Noise, in the technical sense, is a random signal that contains a wide range of frequencies at once. The color name tells you how the energy in that noise is distributed from low to high.

The naming borrows loosely from light. White light contains all visible colors. White noise, by analogy, contains all audible frequencies with equal power at each one. Other colors describe noise that tilts toward the low end or the high end.

White noise

White noise has equal power per frequency across the range you can hear. Because there are many more high frequencies than low ones in each octave, white noise sounds bright and hissy to most people. Think of a radio tuned between stations or a fan on high.

That brightness is part of why white noise is good at masking. It covers a wide band of other sounds, including voices and traffic, by filling in the gaps between them.

Pink noise

Pink noise drops in power as the frequency rises. Specifically, its power falls by about 3 decibels for every octave you go up. Engineers describe it as having equal power per octave, and you'll also see it called 1/f noise.

To the ear, pink noise sounds deeper and softer than white noise. Many people compare it to steady rain or wind in the trees. Because human hearing doesn't treat all frequencies equally, pink noise often sounds more balanced and less harsh than white noise.

Brown noise

Brown noise falls off even more steeply, by about 6 decibels per octave. It's heavy in low frequencies and sounds like a deep rumble: a strong waterfall, distant thunder, or the inside of an airplane cabin.

Despite the name, brown noise has nothing to do with the color brown. It's named after the Scottish botanist Robert Brown, who in 1827 described the random jiggling of pollen particles in water, now called Brownian motion. The mathematical pattern of that motion is what brown noise follows. It's sometimes called red noise, which fits the light analogy, since red light sits at the low frequency end of the visible spectrum.

Other colors you might see

  • Blue noise rises in power with frequency and sounds sharper than white noise.
  • Violet noise rises even more steeply.
  • Green noise has no single agreed technical definition. Apps often use the name for noise focused on the middle frequencies, sometimes described as sounding like nature.
  • Gray noise is adjusted so that it sounds equally loud at all frequencies to the average human ear.

These are less common in sleep apps, and there is very little research on them specifically.

What the research says about sleep

The most common reason people use colored noise is to help them sleep. Here the evidence is limited.

In 2021, a team led by Samantha Riedy published a systematic review in the journal Sleep Medicine Reviews that looked at studies of continuous noise as a sleep aid. They found that the overall quality of evidence was very low. Some studies reported better sleep with noise, others reported no benefit, and a few found that noise could make sleep worse. The authors rated the evidence that continuous noise improves sleep as very low quality, and said more research was needed before promoting it as a sleep aid, especially since it may also harm sleep and hearing.

That doesn't mean noise can't help you. If you live on a busy street or share a wall with a noisy neighbor, steady background sound may mask sudden noises that would otherwise wake you. But the research doesn't show that one color reliably improves sleep for most people.

The pink noise and memory studies

You may have read headlines about pink noise improving deep sleep and memory. Those come from a different kind of research. In a 2017 study published in Frontiers in Human Neuroscience, Nelly Papalambros and colleagues at Northwestern University played short bursts of pink noise to older adults during sleep. The bursts were timed by a computer to match the slow brain waves of deep sleep. The researchers reported that this timed stimulation increased slow wave activity and was linked to better performance on a memory test the next morning.

That is interesting work, but it isn't the same as playing a pink noise track all night. The effect depended on short, carefully timed pulses delivered in a lab, not on continuous background sound.

What the research says about focus

Some people use noise to concentrate, especially in open offices or busy homes. Studies on this are mixed. Background noise can help by masking distracting speech, which is one of the most disruptive sounds for focused work. Some researchers have also studied whether noise helps people with attention difficulties, with varied results.

The honest summary is that noise for focus is worth trying, but your own experience is a better guide than any general claim.

How to choose

Because the research doesn't crown a winner, the best approach is to experiment.

  1. Start with the problem you're solving. If you need to cover voices or traffic, white or pink noise masks a wide range of sound. If high frequencies bother you, try brown noise.
  2. Try each color for a few nights. Give each one at least three nights before deciding. The first night with any new sound can feel strange.
  3. Keep the volume low. You want the noise just loud enough to blend out other sounds. It shouldn't be the loudest thing in the room.
  4. Use a speaker, not earbuds, for sleep when you can. Place it away from your head.
  5. Set a timer if you only need help falling asleep. Many apps let the sound fade out after 30 or 60 minutes.

A note on volume and young children

Volume matters more than color. A 2014 study by Blake Papsin's team at the Hospital for Sick Children in Toronto, published in Pediatrics, measured 14 infant sleep machines at maximum volume. At 30 centimeters, about a foot, every one of them exceeded the 50 decibel limit recommended for hospital nurseries, and three exceeded 85 decibels. The researchers suggested placing machines far from the crib, keeping the volume low and limiting how long they run.

For adults too, long nights of loud sound can add to your total noise exposure. The World Health Organization's safe listening guidance is a good reference.

So which color?

The colors of noise describe real physics: white is even across frequencies, pink tilts gently toward the low end, and brown tilts strongly. The research doesn't show that any one color reliably improves sleep or focus for everyone, and the best known pink noise findings came from timed pulses in a lab. If a steady sound helps you relax or blocks out a noisy world, that is a good enough reason to use it, at a low volume.

Tonight, try pink noise at the lowest volume that covers the sounds outside your window, and notice how you feel in the morning.

If pink noise doesn't suit you, try white or brown on another night and compare how each one feels.

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