# Spectral color

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Color evoked by a single wavelength of light in the visible spectrum

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A [rainbow](/source/Rainbow) is a [decomposition](/source/Dispersion_(optics)) of white light into *all* of the spectral colors.

Laser beams are monochromatic light, thereby exhibiting spectral colors.

A **spectral color** is a [color](/source/Color) that is evoked by [monochromatic light](/source/Monochromatic_radiation), i.e. either a [spectral line](/source/Spectral_line) with a single [wavelength](/source/Wavelength) or [frequency](/source/Frequency) of [light](/source/Light) in the [visible spectrum](/source/Visible_spectrum), or a relatively narrow [spectral band](/source/Spectral_band) (e.g. [lasers](/source/Laser)). Every wave of visible light is perceived as a spectral color; when viewed as a [continuous spectrum](/source/Continuous_spectrum), these colors are seen as the familiar [rainbow](/source/Rainbow). **Non-spectral colors** (or **extra-spectral colors**) are evoked by a combination of spectral colors.

## In color spaces

**[CIE xy chromaticity diagram](/source/CIE_1931_color_space#The_CIE_xy_chromaticity_diagram)**
 The spectrum colors are the colors on the horseshoe-shaped curve on the outside of the diagram. All other colors are not spectral: the bottom line is *the [line of purples](/source/Line_of_purples)*, whilst within the interior of the diagram are unsaturated colors that are various mixtures of a spectral color or a purple color with [white](/source/White), a grayscale color. White is in the central part of the interior of the diagram.

In [color spaces](/source/Color_space) which include all, or most spectral colors, they form a part of boundary of the set of all real colors. When considering a three-[dimensional](/source/Dimension) color space (which includes [luminance](/source/Luminance)), the spectral colors form a [surface](/source/Surface_(mathematics)). When excluding luminance and considering a two-dimensional color space ([chromaticity diagram](/source/Chromaticity_diagram)), the spectral colors form a [curve](/source/Curve) known as the **spectral locus**. For example, the spectral locus of the [CIE xy](/source/CIE_1931_color_space#CIE_xyY) chromaticity diagram contains all the spectral colors (to the eye of the standard observer).

A trichromatic color space is defined by three [primary colors](/source/Primary_color), which can theoretically be spectral colors. In this case, all other colors are inherently non-spectral. In reality, the spectral bandwidth of most primaries means that most color spaces are entirely non-spectral. Due to different chromaticity properties of different spectral segments, and also due to practical limitations of light sources, the actual [distance](/source/Color_distance) between RGB pure [color wheel](/source/Color_wheel) colors and spectral colors shows a complicated dependence on the [hue](/source/Hue). Due to the location of R and G primaries near the 'almost flat' spectral segment, [RGB color space](/source/RGB_color_space) is reasonably good with approximating spectral orange, yellow, and [bright (yellowish) green](/source/Bright_green), but is especially poor in reproducing the visual appearance of spectral colors in the vicinity of central green, and between green and blue, as well as extreme spectral colors approaching [IR](/source/Infrared) or [UV](/source/Ultraviolet).

Spectral colors are universally included in [scientific](/source/Color_science) color spaces such as CIE 1931, but industrial and consumer color spaces/models such as [sRGB](/source/SRGB), [CMYK](/source/CMYK), and [Pantone](/source/Pantone_Matching_System), do not typically include any spectral colors. Exceptions include [Rec. 2020](/source/Rec._2020), which uses three spectral colors as primaries (and therefore only includes precisely those three spectral colors), and color spaces such as the [ProPhoto RGB color space](/source/ProPhoto_RGB_color_space) which use imaginary colors as primaries.

In color spaces such as [CIELUV](/source/CIELUV), a spectral color has maximal [saturation](/source/Colorfulness#Saturation). In [Helmholtz coordinates](/source/Helmholtz%E2%80%93Kohlrausch_effect#Helmholtz_color_coordinates), this is described as 100% [purity](/source/Colorfulness#Excitation_purity).

### In dichromatic color spaces

In [dichromatic](/source/Dichromacy) [color vision](/source/Color_vision) there is no distinction between spectral and non-spectral colors. Their entire visible [gamut](/source/Gamut) can be represented by spectral colors.[note 1]

## Spectral color terms

The spectrum is often divided into *[color terms](/source/Color_term)* or names, but aligning boundaries between color terms to a specific wavelength is very subjective.

The first person to decompose white light and name the spectral colors was [Isaac Newton](/source/Isaac_Newton), in the 1660s.[1] Early in the study of radiometry, Newton was not able to measure the wavelength of the light, but his experiments were repeated contemporarily to estimate wavelengths where his color term boundaries probably lay.[2] [Newton's](/source/Isaac_Newton) color terms included red, orange, yellow, green, blue, indigo, and violet; this color sequence is still used to describe spectral colors colloquially and a [mnemonic](/source/Mnemonic) for it is commonly known as "[Roy G. Biv](/source/Roy_G._Biv)".

In modern divisions of the spectrum, [indigo is often omitted](/source/Indigo#Isaac_Newton's_classification_of_indigo_as_a_spectral_color) and [cyan](/source/Cyan) is often included. Some have argued that Newton's indigo would be equivalent to modern blue, and his blue equivalent to cyan.[3] However, a more recent explanation is that Newton was working by analogy with the musical scale.[2] In the table below, note how wavelength is not proportional to a perceptually uniform hue scale. On the other hand, Newton's sections include five which are approximately uniform in size as they would have physically appeared in the diffracted spectrum, and two which were approximately half the size of the others, namely orange and indigo. This corresponds in size and location to the five whole tones and two semitones of the musical scale in [Dorian mode](/source/Dorian_mode). In contrast, the sections in the [ISCC-NBS](/source/ISCC-NBS) spectrum vary greatly in wavelength range, but are more consistent in the [hue](/source/Hue) degree range. Both instances deviate from the [basic color terms](/source/Color_term#Basic_color_terms) used in English, only some of which are spectral colors.

The table below includes several definitions where the spectral colors have been categorized in [color terms](/source/Color_term). The "Approximate appearance" column displays the color with the same [OKLCh](/source/OKLab) hue and [lightness](/source/Lightness) as the corresponding spectral color for that wavelength, with maximal [sRGB](/source/SRGB) saturation, given a spectrum of equal [radiant power](/source/Radiant_power) and with the highest brightness as to, when projected onto sRGB, still have maximal saturation within this [color gamut](/source/Gamut). [Gamut mapping](/source/Gamut_mapping) is necessary because displays cannot produce all, if any, spectral colors (a display with sRGB gamut and [D65 whitepoint](/source/Standard_illuminant#Illuminant_series_D) is assumed for this approximation). The colors at the ends of the spectrum are shown as dark since the [cone cells](/source/Cone_cells) in the eye are progressively less sensitive to light as the extremes of the visible spectrum are approached.

Spectral color classifications Wavelength (nm) Approximate appearance Newton[2] ISCC-NBS[4] Malacara[5] CRC Handbook[6] 1700 1943 2011 2006 380 Violet Violet Violet Violet 390 400 410 420 430 Indigo Blue 440 Blue 450 Blue Blue 460 470 480 490 Green Blue-green 500 Green Cyan Green 510 520 Green 530 Yellow 540 550 Yellow-green 560 570 Yellow Yellow 580 Orange Yellow Orange 590 Orange Orange 600 610 Red 620 Red Red 630 Red 640 650 660 670 680 690 700 710 720 730 740

## Extra-spectral colors

Among some of the colors that are *not* spectral colors are:

- [Grayscale](/source/Grayscale) (achromatic) colors, such as [white](/source/White), [gray](/source/Grey), and [black](/source/Black).

- Any color obtained by mixing a gray-scale color and another real color (either spectral or not), such as [pink](/source/Pink) (a mixture of a [reddish](/source/Red) color and white), or [brown](/source/Brown) (a mixture of [orange](/source/Orange_(color)) and black or gray).

- [Violet](/source/Violet_(color))-[red](/source/Red) colors, which include colors in the [line of purples](/source/Line_of_purples) (such as [magenta](/source/Magenta) and [rose](/source/Rose_(color))), and other variations of purple and red.

- [Impossible colors](/source/Impossible_color), which cannot be seen under normal viewing of light, such as over-saturated colors or colors that are seemingly brighter than white.

- [Metallic colors](/source/Metallic_color) which reflect light by effect.

## Notes

1. **[^](#cite_ref-1)** This is true for dichromats with [photoreceptor cells](/source/Photoreceptor_cell) with overlapping [spectral sensitivity](/source/Spectral_sensitivity) curves. If the spectral sensitivity curves do not overlap, then all colors (except the ones that only excite one type of conecell) would be non-spectral. However, there are no known vision systems where the [cones'](/source/Cone_cell) spectral sensitivity curves do not overlap.

## References

1. **[^](#cite_ref-2)** ["Newton and the Science of Color"](https://www.thecolumbiasciencereview.com/blog/newton-and-the-science-of-color). *Columbia Science Review*. Retrieved May 2, 2025.

1. ^ [***a***](#cite_ref-mclaren_3-0) [***b***](#cite_ref-mclaren_3-1) [***c***](#cite_ref-mclaren_3-2) McLaren, K. (1985). "Newton's indigo". *Color Research & Application*. **10** (4): 225–229. [doi](/source/Doi_(identifier)):[10.1002/col.5080100411](https://doi.org/10.1002%2Fcol.5080100411).

1. **[^](#cite_ref-4)** MacAdam, David L. (May 1, 1975). ["Color essays*"](https://opg.optica.org/abstract.cfm?URI=josa-65-5-483). *Journal of the Optical Society of America*. **65** (5): 483–493. [doi](/source/Doi_(identifier)):[10.1364/JOSA.65.000483](https://doi.org/10.1364%2FJOSA.65.000483). [ISSN](/source/ISSN_(identifier)) [0030-3941](https://search.worldcat.org/issn/0030-3941).

1. **[^](#cite_ref-5)** Kelly, Kenneth L. (November 1, 1943). "Color Designations for Lights". *Journal of the Optical Society of America*. **33** (11): 627. [doi](/source/Doi_(identifier)):[10.1364/JOSA.33.000627](https://doi.org/10.1364%2FJOSA.33.000627).

1. **[^](#cite_ref-6)** Malacara, Daniel (2011). *Color vision and colorimetry : theory and applications* (2nd ed.). Bellingham, Wash.: SPIE. [ISBN](/source/ISBN_(identifier)) [9780819483973](https://en.wikipedia.org/wiki/Special:BookSources/9780819483973).

1. **[^](#cite_ref-7)** Bruno, Thomas J. (2006). *CRC handbook of fundamental spectroscopic correlation charts*. Boca Raton, FL: CRC Press. [ISBN](/source/ISBN_(identifier)) [9780849332500](https://en.wikipedia.org/wiki/Special:BookSources/9780849332500).

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Adapted from the Wikipedia article [Spectral color](https://en.wikipedia.org/wiki/Spectral_color) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Spectral_color?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.