Pitch-to-Color Standard

The premise is straightforward, and it is arithmetic rather than opinion. Every pitch has exactly one color: not a color an artist assigned to it because it seemed fitting, but one computed from the pitch's frequency by a fixed rule that anyone can verify. In twelve-tone equal temperament there are twelve pitch classes per octave, and therefore twelve canonical colors — identical in every application, instrument, and implementation that conforms to this standard. The equal-tempered piano serves throughout this document as the worked example and reference grid. It is not the boundary of the standard: as set out below, PCS is defined continuously for any frequency.

One consequence follows immediately: a chord is a ready-made color palette. A chord is a set of pitch classes sounded together, and each contributes its color. Take B minor — the pitch classes B, D, and F♯:

It should therefore be possible to specify “use Bm as my color palette” — to a design program, a website builder, or an AI assistant — and receive exactly those three colors in return: yellow-green, blue, and deep red. Not an interpretation and not a mood; the same result every time, because the pitch classes determine it.

One qualification belongs at the front, not in a footnote. The canonical colors are the pure spectrum, and the pure spectrum is bright — by definition, the way a note at fortissimo is loud by definition. In practice nobody plays every note at full volume, and nobody designs with the raw spectrum: you shade. Two controls do the shading, and neither ever touches the hue, so a shaded color never stops being its pitch. Brightness runs along the dynamics ladder — pp, p, mp, mf, f, ff — with mf the canonical color itself. Mute adds grey in named steps: Grey-0 is the true color — no grey added — and each higher step, Grey-1, Grey-2, Grey-3, adds more grey, drawing saturation down toward grey. (The steps were written G0–G3 in v1.0; those short forms remain recognised aliases — in this document, in exports, and in the conformance checker — so existing palettes keep working.) Read side by side, the same B minor palette as reference and as it is actually used:

Shading tames the palette without dissolving it. The yellow-green becomes an olive — taken to pp it deepens to #3A5700, still unmistakably B. The blue settles into deep navy, in the family of #003157 at the dark end. And the red, deep to begin with, holds its strength, which is exactly why it is the color that carries the accent in worked examples — a button, an emblem, a second hand. The shade control in §4 produces every step of both axes for any pitch color, each with its exact hex.

The same principle applies to instruments. Piano keys can carry the color of the pitch they produce — and because color belongs to the pitch class rather than to any single position on the keyboard, the pattern repeats identically in every octave:

One octave

The next octave — the same colors again

Applied from the beginning of musical training, keys like these make the pairing continuous: a learner hears a pitch and sees its color at the same moment, on every repetition, in every octave, from the first lesson onward. Sustained pairing of that kind could plausibly build a strong, automatic sound–color association. Whether systematic training can produce something comparable to developmental synesthesia is an open empirical question, and this standard does not claim to create innate synesthesia. What it does supply is the precondition any such program would require — pairings that are fixed, consistent, and identical across instruments and environments, so that what is learned on one piano remains true on every other.

The domain of the standard deserves to be stated precisely. PCS is defined for any frequency, not only for the twelve equal-tempered pitch classes. A frequency that falls between two pitch classes — a microtone, a quarter-tone inflection, a deliberately detuned string — is not outside the standard. It is mapped by the same octave-doubling rule to its own wavelength, and it is reported as its nearest equal-tempered pitch together with a signed deviation in cents (a cent is one hundredth of a semitone). A tone at 453 Hz, for example, is A +50¢ — a quarter-tone — and its color lies that far along the spectrum between the canonical colors of A and A♯. Interpolated colors of this kind are computed from the exact frequency, never rounded to the nearest note; the converter in §3 resolves any frequency this way.

The same treatment covers the frequencies named by sacred and contemplative traditions, including those associated with the chakras. Entered by their exact value in hertz, such a frequency returns a nearest pitch, a signed cents deviation, and a continuous PCS color — 528 Hz, for instance, resolves to C +16¢ and to the hue that implies. These designations are traditional and attributed: the standard records them as labels and assigns them colors by the same rule as every other frequency, but it makes no claim that any frequency produces a healing or physiological effect, and no such effect should be read here as scientifically established.

Everything that follows is the technical reference: the formulas, the canonical table, and the conformance tests by which builders, software, and AI systems produce exactly these colors and demonstrate that they have done so. Readers who need only the concept have it; implementers should read on.

Sound and light are both frequencies; they simply live many octaves apart. This standard fixes the bridge between them. A pitch is doubled — multiplied by two, again and again, which never changes what note it is — until its frequency reaches this standard's reference band of light. That optical frequency, expressed as a wavelength, is the pitch's color under this standard.

Because the rule is arithmetic rather than taste, two products that implement it always agree: an E is the same violet in a tuner, a mandala generator, a stage-lighting rig, and a textbook. The standard defines the physical mapping (normative), one canonical sRGB value for each pitch class (normative chosen constants, for screens), and a conformance test anyone can run. It asks for no permission and charges no fee; adoption is the whole point.

An octave is a doubling. A4 at 440 Hz, doubled once, is A5 at 880 Hz — the same note, higher. Doubling preserves pitch class all the way up, so there is exactly one place in the visible spectrum where each pitch class lands. The standard fixes the destination as one reference optical octave, 400–800 THz, and the anchor as A4 = 440 Hz in twelve-tone equal temperament.

One range, stated honestly, and used everywhere in this document — text, spectrum bar, and converter alike: 400–800 THz ≈ 375–750 nm, one reference optical octave. The band is fixed because it is exactly one octave, so pitch classes land in it the way they land in any octave. Its short-wavelength end, ≈375 nm, lies at the boundary where visible violet gives way to UV-A and the eye's sensitivity is faint; PCS does not claim the whole band is equally visible, only that it is the octave the mapping is defined on.

The famous “40 octaves” is exact for A. For pitch classes C through F the count is 41, because the destination band — not the count — is what the standard fixes. The result is identical either way: every octave of a note maps to the same color, and enharmonic spellings (C♯ and D♭) are the same pitch class and the same color.

Twelve pitch classes, twelve wavelengths. Rising chromatically from A, wavelength shortens through the spectrum — orange, yellow, green, blue, violet — until F, after which the next semitone would leave the reference band and wraps one optical octave lower to F♯, deep red. The wheel closes on itself, exactly as the chromatic scale does.

Reference pitches are given in octave 4; the mapping is octave-invariant, so any octave of the note gives the same row. Physical values are rounded to the precision shown; the hex constants are exact — conformance is defined in §5.

The mapping is continuous, not just a table. Enter any frequency — or tap a piano key — and the standard resolves it wavelength-first: the frequency is octave-reduced to its exact wavelength, and the color is read from that wavelength. Between pitch classes the color is interpolated along the spectrum and is an approximation — only the twelve §2 constants are exact. Across the F–F♯ wrap there is no interpolation at all: as frequency rises past F the wavelength falls toward the ≈375 nm band edge, then jumps a full optical octave to ≈750 nm and deep red. The jump is shown, never blended. Any of those colors can then be shaded or muted in place, hue untouched. The mapping also runs backwards: the reverse lookup below takes any color and returns its wavelength, its exact frequency, and its sound.

Reverse lookup — color to sound

The converter above runs pitch → color; this one runs it back. Pick any color and it is read at the nearest point on the same color path the converter draws — the F–F♯ wrap included, so deep violet and deep red are never blended or confused. The frequency is exact and continuous: microtones are reported, never snapped to the nearest note. Brightness is amplitude in PCS, so the color's lightness also names its dynamic. True neutrals — white, black, pure greys — have no hue, and therefore no pitch.

Pick a color

Hex value

Play this color

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Image eyedropper · pick a color from a photo

Upload any image — on a phone, the picker opens your photo library — then tap or click any point on it. The color there, averaged over a small area around the tap, is fed straight into this lookup: the swatch and hex field above take the sampled color, and the wavelength, frequency, nearest pitch, and Play button below all follow.

Upload an image

Wavelength

619.7 nm

Audio frequency

440.00 Hz

Nearest pitch

A4

Deviation

0 cents

Implied dynamic

mf · true

True color at this λ (mf)

#FF7800

A chord is a set of pitch classes, so under this standard every chord is also a color palette — the same one, everywhere, every time. Build one and read it both ways. A minor is red-orange, green, and violet; that is not an interpretation, it is arithmetic.

A standard nobody can test is a suggestion. An implementation conforms when it reproduces the canonical wavelengths within tolerance and renders each pitch class at its §2 canonical sRGB value, or within ΔE*_ab ≤ 3 of it. That test measures agreement with the §2 table — the standard's chosen constants — not fidelity to monochromatic light, which no screen can emit. The three test vectors below exercise the anchor, the violet end, and the wrap at F♯.

Everything an implementer needs, in copyable form. The CSS variables carry the reference palette; the JSON and CSV downloads carry the full canonical table, wavelengths included.

1. MustAnchor tuning at A4 = 440 Hz and derive pitch frequencies by twelve-tone equal temperament, f = 440 · 2^(m−69)/12.

2. MustReduce each pitch frequency by exact powers of two into the reference optical band 400 THz ≤ f < 800 THz. Approximate or perceptual rescaling is not conforming.

3. MustCompute wavelength as λ = c / f with c = 299,792,458 m/s, and report it in nanometers.

4. MustAssign color by pitch class only. Octave, register, instrument, and spelling (C♯ vs D♭) must never change a note's color.

5. MustFor screen display, use the §2 canonical sRGB constant for each pitch class, or a value within ΔE*_ab ≤ 3 of it.

6. MustAlways pair color with the note name in interfaces. Color is a channel, never the only label — roughly 1 in 12 men cannot distinguish some of these hues by eye.

7. ShouldWhen a product implements this standard, say so in its credits or settings: “Pitch colors: Pitch-to-Color Standard v1.1.” Attribution is how a standard stays one standard.

• Screens approximate light. No display emits monochromatic 619.7 nm light. The §2 hex values are normative constants chosen as readable screen approximations of the mapped wavelengths; conformance is agreement with those constants (§5), not spectral fidelity. The wavelength is the physical statement; the hex is the standard's fixed value for it.
• Tuning is an input, not a detail. The mapping is defined at A440. A pitch at A442 is +8 cents sharp and still maps to A — the converter in §3 shows exactly where any real frequency lands.
• Microtones map continuously. The canonical table names the twelve pitch classes of equal temperament, but the formula in §1 assigns a wavelength to any frequency whatsoever.
• This is a correspondence, not a claim about perception. Synesthetes each experience their own colors, and this standard neither matches nor overrides them. It is a shared convention grounded in octave equivalence — the same kind of agreement that makes A440 a standard: chosen once, openly, so everyone can build on it.
• Versioning. The physical mapping in §1–§2 is fixed for v1.x. Any future change to anchor, band, or canonical values requires a new major version; v1.x values will never be silently revised — every revision is dated and logged in the revision history. (v1.1 changed no canonical value.)

Nature rarely sounds exactly on a note — and under this standard it does not have to. Every frequency below is given exactly as reported in its source, never rounded to the note, transposed by whole octaves (which never changes pitch class), and placed against the nearest equal-tempered pitch at A4 = 440 Hz. The deviation is signed cents — 1200·log₂(f_transposed ÷ f_target); ±50¢ is a quarter-tone. A frequency between notes still has a color: its true color is the hue that far along the spectrum between the two neighbouring pitch-class colors, beside the canonical color of its nearest note. Values researched 14 October 2026; hedges and disagreements in the sources are carried, not smoothed away.

Strongest documented resonance for each pitch class

One primary phenomenon per pitch class — the strongest, narrowest documented match found. C♯ and F♯ are honest weak spots: no narrow resonance within about ±25¢ was found for either, and their closest candidates are flagged as such.

More exact frequencies worth citing

• Earth's fundamental spheroidal mode ₀S₂ — 309.286 µHz (exact eigenfrequency as reported) → ×2²⁰ = 324.3 Hz → E, −28¢ · true color #5C00F0, 420.4 nm. Earth's wider “hum” is ~50 discrete modes between ~2 and 7 mHz spanning more than an octave of pitch classes — no single note exists for the hum as a whole. Source
• Crab pulsar — 29.946923 Hz at epoch MJD 48442.5 → ×16 = 479.151 Hz → A♯, +48¢ · true color #D6F700, 569.0 nm — almost exactly a quarter-tone, the ideal in-between color. It spins down ≈ −0.69¢/yr; an extrapolation to 2026 (ignoring glitches) gives ~29.53 Hz → A♯, +23¢ — an estimate, not a measurement. Source: MNRAS
• Brood X cicada chorus — 1,330 Hz, a single strong spectral peak → ÷4 = 332.5 Hz → E, +15¢ · true color #7A00DE, 410.0 nm. The peak wandered 1,200–1,500 Hz with temperature. Source: ScienceDaily
• Ocean secondary microseism — about 0.15 Hz, the strongest ambient seismic signal → ×2048 = 307.2 Hz → D♯, −22¢ · true color #0C1FFF, 443.8 nm. Approximate, broad peak; its 0.1–0.3 Hz band spans more than an octave. Source: PNAS
• Antarctic blue-whale Z-call, Unit A — 27.7 Hz in 2002 → ×16 = 443.2 Hz → A, +13¢, falling 0.135 ± 0.003 Hz/yr; by 2010 it was 26.6 Hz → G♯, +43¢. A note that is measurably sliding between pitch classes. Source: Gavrilov et al.
• The Sun has no single note. Its 5-minute oscillations are a spectrum (~1–5 mHz), not a line: power peak 3.1 mHz → G♯, −38¢; measured central frequency ~3.23 mHz → G♯, +34¢. The envelope is broad enough that both readings appear — do not assign the Sun one pitch.

Unison — many sources locked to one frequency

• Schumann resonance — ~50 lightning strikes/sec worldwide continuously excite the same cavity modes: one planetary chorus (modes listed in the table above).
• Periodical cicada choruses — the Brood X chorus showed a single strong peak at 1,330 Hz → E, +15¢; Magicicada cassini and M. tredecassini synchronise their calling rhythm in true unison, neighbouring groups adjusting rate to match.
• Booming sand dunes — millions of grains phase-lock to one dominant tone per dune, 70–105 Hz → C♯, +18¢ to G♯, +20¢ across sites, continuously crossing every pitch class in between; each dune locks to its own note.
• Mosquito duet — a pair converges on a shared harmonic measured at 1,354.5 Hz → E, +47¢, from a female fundamental of 430.6 Hz → A, −37¢ and a male 636.7 Hz → D♯, +40¢. (Press coverage rounds these to ~400 / ~600 / ~1,200 Hz, which lands on the wrong pitch classes.)
• Counter-example — frogs mostly do not sing in unison. Japanese tree frogs phase-lock mainly in anti-phase; spring peepers alternate with neighbours. The synchrony is real; the unison is not.

Claims that do not hold up

• “432 Hz = nature's frequency” — myth. A Reuters fact-check found no empirical basis for a preferred cosmic frequency; historical pitch wandered ~390–480 Hz. In this standard's arithmetic 432 Hz is simply A, −32¢, and octave-transposing Schumann's 7.83 Hz gives B (+25¢), never 432. Source: Reuters
• “Solfeggio frequencies” — modern invention (1970s numerology). For reference, 528 Hz → C, +16¢ — an ordinary pitch class, with no measured natural resonance or healing effect.
• Schumann wellness claims — unsupported. The resonance is real, but electromagnetic, picotesla-faint, and variable — its fundamental alone spans three pitch classes in a day.

Open questions, stated plainly: C♯ and F♯ have no narrow documented resonance within ~±25¢; published Schumann mode lists disagree by ~1 Hz (30–90¢ at these transpositions) and both readings are reported above rather than averaged; Perseus cents are not computable beyond the ~36¢ uncertainty shown; broadband phenomena (dune ranges, Earth's hum band, microseism band) have endpoint cents at best, never a single value.

Pitch–colour correspondence is an old idea, and the octave bridge at the heart of this standard is older still. This section exists so the record is straight about what PCS did not invent.

• Isaac Newton, Opticks (1704) — divided the spectrum into seven colours by explicit analogy with the seven tones of the musical scale, tying the width of each colour band to musical intervals. The first published pitch–colour mapping, and the ancestor of every closed colour wheel of tones since.
• A. Wallace Rimington and the colour organ (1890s) — built instruments to perform colour as music is performed, and argued for a fixed correspondence between the spectrum and the chromatic scale.
• Alexander Scriabin, Prometheus: The Poem of Fire (1910) — scored a part for tastiera per luce, a colour keyboard, mapping keys to colours around a circle-of-fifths scheme. An artist's personal synesthetic system, published as part of the work.
• Hans Cousto, The Cosmic Octave (Die Kosmische Oktave, 1984; English edition 1988) — the direct methodological predecessor of §1. Cousto's method transposes real periodic phenomena — planetary orbits, molecular and atomic frequencies — by successive octave multiplication into the audible range, and extends the same transposition into the visible band to derive colours. PCS applies the identical octave-transposition arithmetic in the opposite direction of travel: from pitch upward into light.
• Wavelength-to-colour renderings in software — published approximations that turn a wavelength into an RGB value (Dan Bruton's widely used algorithm is the best known) predate PCS and are one reason §2 fixes its own constants instead: those approximations disagree with each other, so a standard that pointed at them would not be one standard.

What PCS claims as its own is correspondingly narrow: the fixed canonical table of twelve sRGB constants in §2; the ΔE*_ab ≤ 3 conformance test measured against that table (§5); and the convention of reporting any frequency continuously, as a nearest pitch class plus a signed deviation in cents (§3, §9). The octave bridge itself is prior art, centuries old, and is not claimed.

This appendix is non-normative: it is not part of the standard, and nothing in it is required, tested, or endorsed. It is kept separate from the documented natural frequencies of §9. Author Lynne McTaggart discusses a set of frequencies she calls “God Notes”. As of October 2026, only one value — 110 Hz — could be verified from publicly available sources; the remaining values appear only inside her book and buyer-only material, so they are not listed here. Every use in the right-hand column is McTaggart’s claim, attributed to her, not an established effect, and this standard endorses none of them. What the standard does supply is the pitch and color 110 Hz maps to by the same rule as every other frequency — and 110 Hz happens to land exactly on the anchor’s own pitch class, two octaves below A4.

v1.1 — October 25, 2026

• §3 — reverse color-to-sound lookup added. Alongside the frequency→color converter, a second tool now runs the mapping backwards: pick any color (picker or typed hex) and it reports the color's wavelength on the 375–750 nm reference optical octave, its exact audio frequency — the light frequency octave-reduced into the audible range, continuous, microtones included, never snapped to a note — the nearest pitch with its signed deviation in cents, and the nearest dynamic (pp–ff) implied by the color's brightness, brightness being amplitude in PCS; a Play button sounds the exact frequency. The lookup inverts the converter's own color path, so its answers agree with the §2 canonical table and the F–F♯ wrap stays a discontinuity — deep violet and deep red are never blended or confused. A true neutral color (white, black, a pure grey) has no hue and is reported plainly as having no pitch. No canonical hex, wavelength, or formula changed.
• §3 — image eyedropper added to the reverse lookup. The reverse lookup now also takes its color from a photograph: upload any image (on a phone, the file picker opens the photo library), and tapping or clicking any point samples that pixel's color — averaged over a small area around the tap for stability — and feeds it into the same readouts and Play button, with a marker left on the image where the sample was taken and the picked-color swatch and hex field updated to match. Sampling reads the image through a canvas rather than the desktop-only EyeDropper API, so it works in phone and in-app browsers as well.

v1.1 — October 22, 2026

• No canonical value changed. The twelve §2 hex constants, the wavelengths, and the pitch→wavelength formulas of §1 are identical to v1.0; published palettes built on v1.0 remain conforming.
• §2, §5, §8 — the hexes are stated as what they are. The twelve sRGB values are now framed explicitly as normative chosen constants; the ΔE*_ab ≤ 3 conformance test is defined as agreement with the §2 table, not spectral fidelity; and the v1.0 contradiction between “brightness-normalized” (§2) and “faithful renderings” (§8) is removed.
• §3 — the converter is wavelength-first. Color is read from the exact wavelength; the F–F♯ wrap is treated as the discontinuity it is — wavelength falls toward ≈375 nm, then jumps to ≈750 nm, with no blending between F (#820097) and F♯ (#A80000). Remaining between-note interpolations are labelled approximations.
• §1, §2 — one band, stated once. 400–800 THz ≈ 375–750 nm is given throughout as a reference optical octave whose short-wavelength end lies at the UV-A / violet boundary; the spectrum bar's scale, gradient, and marker positions are aligned to the same 375–750 nm range (v1.0's bar silently used 380 nm).
• Prior art. A Prior art & references section is added, citing Cousto's Cosmic Octave octave-transposition method and earlier pitch–colour correspondences; the standard's own claim is restated as limited to its canonical table, its conformance test, and cents reporting.
• Mute steps renamed. G0–G3 are now Grey-0…Grey-3, removing the collision with pitch names such as G1 and G2; the G-forms remain recognised aliases in text, exports, and the checker.
• McTaggart “God Notes” relocated. The entry moves from §9 to non-normative Appendix A, with its segregation, attribution, “not established” flag, and the 110 Hz → A2 → #FF7800 mapping unchanged. §9's documented frequencies are otherwise untouched.
• Dating. The document now carries its revision date and this changelog; v1.0's text did not record that §9 values were researched after the publication date.

v1.0 — October 13, 2026

Original publication of the Pitch-to-Color Standard: the §1 octave-doubling principle, the §2 canonical table, the §3 converter, the §4 palette and shading tools, the §5 conformance test and checker, implementation data, requirements, scope, and the documented natural frequencies of §9 (§9 values researched 14 October 2026).