Three words used almost interchangeably online. They have exact definitions, and the difference is audible in about four seconds.
Most people arrive at this by searching one colour, trying it, and finding it is not the sound they had in their head. Usually they wanted a different colour and did not know the word for it.
All three are broadband noise. What separates them is the slope: how the energy falls away as the frequency rises.
Equal power at every frequency. Flat on a meter, bright and hissy to an ear. Think of an untuned radio, or air escaping.
Falls 3 decibels per octave, which works out as equal power in every octave. Fuller and more even than white, without the top-end hiss. Steady rain and distant surf sit near here.
Falls 6 decibels per octave, twice as steep again. Deep and dark, more felt than heard. A waterfall through a wall, a ship's engine room, the inside of a plane.
This is the part that surprises people, and it explains the whole family. Equal power per hertz is not equal power to a human ear, because hearing works in octaves and each octave upward covers twice as many hertz as the one below it. The octave from 5,000 to 10,000 hertz contains as much bandwidth as everything below 5,000 put together.
So a spectrum that is flat on paper puts most of its energy in the top few octaves, which is where hiss lives. White noise measures flat and hears bright. Pink noise corrects for exactly that, which is why it is the one that sounds "even" to most people, and why it is the reference engineers use when they tune a room.
Brown goes past even and lands on dark. Nothing is wrong with any of them. They are three points on one slope, and which one sounds right to you is a matter of ears.
White, pink and brown are defined by their slope, so two apps using the words correctly will sound alike. The rest are not.
Here is the practical problem, and it is worth knowing before you judge a colour by one app. A great deal of what is sold under these names is a recording with a filter on it: someone took a hiss or a fan or a stretch of rain and pulled the treble down until it sounded about right.
That is labelling by feel. It gets you something in the neighbourhood, and it also gets you a spectrum nobody measured, uneven level between one track and the next, and a short recording looping with an audible seam where the end meets the start. Once you hear the seam you cannot stop hearing it, and then you are lying there waiting for it instead of forgetting the sound is on.
Noise is one of the few things in audio that can simply be generated to its definition. When it is, the colour is the colour, and it can run as long as you like without a join.
The internet is confident about this and it should not be. Brown noise in particular has been attached to a lot of claims in the last few years, and the research underneath them is thin: the studies are small, they measure different things, and they disagree. There is no established finding that one colour outperforms another for sleep, for focus, or for anyone in particular.
So Luten is not going to tell you which one works. What can be said without stretching anything is smaller and more useful:
Faster than reading about it, and it is your ears that have to agree, not a chart.
In that order, without changing the volume. The slope is obvious when you hear the three in sequence and almost invisible when you hear one alone.
That is the whole test. The right one is not the one that sounds best in the first four seconds, it is the one that disappears.
The colours change character when quiet. Brown thins out, white gets harsher relative to everything else.
The end is where the loop either joins cleanly or does not, and where an outro voice would live. It is the least tested part of any sound app.
Luten is sound for the mind, and noise is the part of the catalog where the engineering is checkable rather than a matter of taste.
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They differ in how the energy is spread across frequency. White noise has equal power at every frequency, so the high end dominates and it reads as bright and hissy. Pink noise rolls the top off at 3 decibels per octave, which puts equal power in every octave and sounds more balanced. Brown noise rolls it off twice as steeply, at 6 decibels per octave, which is why it sounds deep and distant, closer to a waterfall heard through a wall than to a radio between stations.
There is no established answer, and anyone who gives you one is going further than the evidence does. The comparisons between noise colours are thin, and what exists is mostly small and mixed. What is not in doubt is that people's preferences differ a great deal. The useful test is your own ears over a few nights, not a chart.
Green noise has no standard engineering definition, unlike white, pink and brown, which are defined by their spectral slope. It is an audio and marketing term, usually meaning noise weighted toward the middle of the range, around 500 hertz, where a lot of natural ambience sits. Worth knowing when you see it sold as a distinct thing.
Because equal power per hertz is not equal power to a human ear. Hearing works in octaves, and each octave upward covers twice the range of hertz as the one below it, so the top octaves carry most of the energy in a flat spectrum. White noise measures flat and hears bright. That is not a fault in the sound, it is the difference between a measurement and an ear.
Yes, all three, along with variants of each: white noise warmed, softened, widened or slowly breathing, and the same kind of variation elsewhere. They are synthesised to a measured spectral slope rather than made by taking a recording and pulling the treble off it.
Also worth reading: sleep sounds with no talking and sounds for waking up at 3am.