Editing Spectral color (section)

== In color spaces==
[[File:CIE1931xy blank.svg|right|thumb|
{{center|'''[[CIE 1931 color space#The CIE xy chromaticity diagram|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]]'', whilst within the interior of the diagram are unsaturated colors that are various mixtures of a spectral color or a purple color with [[white]], a grayscale color. White is in the central part of the interior of the diagram, since [[Additive colors|when all colors of light are mixed together, they produce white]].]]

In [[color space]]s which include all, or most spectral colors, they form a part of boundary of the set of all real colors. When considering a three-[[dimension]]al color space (which includes [[luminance]]), the spectral colors form a [[surface (mathematics)|surface]]. When excluding luminance and considering a two-dimensional color space ([[chromaticity diagram]]), the spectral colors form a [[curve]] known as the '''spectral locus'''. For example, the spectral locus of the [[CIE 1931 color space#CIE xyY|CIE xy]] chromaticity diagram contains all the spectral colors (to the eye of the standard observer).

A trichromatic color space is defined by three [[primary color]]s, 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 [[color distance|distance]] between RGB pure [[color wheel]] colors and spectral colors shows a complicated dependence on the [[hue]]. Due to the location of R and G primaries near the 'almost flat' spectral segment, [[RGB color space]] is reasonably good with approximating spectral orange, yellow, and [[bright green|bright (yellowish) green]], {{anchor|×}}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 [[Infrared|IR]] or [[ultraviolet|UV]].

Spectral colors are universally included in [[color science|scientific]] color spaces such as CIE 1931, but industrial and consumer color spaces/models such as sRGB, CMYK, and [[Pantone Matching System|Pantone]], do not typically include any spectral colors. Exceptions include [[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]] which use imaginary colors as primaries.

In color spaces such as [[CIELUV]], a spectral color has maximal [[Colorfulness#Saturation|saturation]]. In [[Helmholtz–Kohlrausch effect#Helmholtz color coordinates|Helmholtz coordinates]], this is described as 100% [[Colorfulness#Excitation_purity|purity]].

===In dichromatic color spaces===
In [[Dichromacy|dichromatic]] [[color vision]] there is no distinction between spectral and non-spectral colors. Their entire gamut can be represented by spectral colors.{{NoteTag|This is true for dichromats with [[photoreceptor cell]]s with overlapping [[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 [[cone cell|cones']] spectral sensitivity curves do not overlap.}}