Editing Natural Color System (section)

== Definition ==
The NCS states that there are six elementary [[color]] percepts of human vision—which might coincide with the [[primary color#Psychological primaries|psychological primaries]]—as proposed by the hypothesis of [[color opponency]]: [[white]], [[black]], [[red]], [[yellow]], [[green]], and [[blue]]. The last four are also called [[unique hues]]. In the NCS all six are defined as elementary colors, irreducible [[qualia]], each of which would be impossible to define in terms of the other elementary colors. All other experienced colors are considered composite perceptions, i.e. experiences that can be defined in terms of similarity to the six elementary colors. E.g., a saturated [[pink]] would be fully defined by its visual similarity to red, blue, black and white.<ref name=":0" />

Colors in the NCS are defined by three values, expressed in [[percentage]]s, specifying the degree of blackness (''s'', = relative visual similarity to the black elementary color), [[Chromaticity|chromaticness]] (''c'', = relative visual similarity to the "strongest", most saturated, color in that hue triangle), and [[hue]] (''Φ'', = relative similarity to one or two of the chromatic elementary colors red, yellow, green and blue, expressed in at most two percentages). This means that a color can be expressed as either Y (yellow), YR (yellow with a red component), R (red), RB (red with a blue component), B (blue), etc. No hue is considered to have visual similarity to both hues of an opponent pair; i.e., there is no "redgreen" or "yellowblue". The blackness and the chromaticness together add up to less than or equal to 100%. The remainder from 100%, if any, gives the amount of whiteness (''w'').<ref name=":0" /> [[Achromatic colors]], i.e., colors that lack chromatic contents (ranging from black, to grey and finally white), have their hue component replaced with a capital "N"; for example, {{colorsample|#191919|description=sample of S9000N}} "NCS S 9000-N" (a more or less complete black). NCS color notations are sometimes prepended by a capital "S", which denotes that the current version of the NCS color standard was used to specify the color.

In summary, the NCS color notation for {{colorsample|#D38E87|description=sample of S2030Y90R}} '''S 2030-Y90R''' (light, pinkish red) is described as follows.

: <math>
\underset{\begin{matrix} \vphantom{|^|}\text{NCS 1950} \\[-4mu] \text{Standard} \end{matrix}} { \text{S} } \quad 
\underbrace{\underset{\vphantom{|^|}s}{20}\ \underset{\vphantom{|^|}c}{30}}_{\text{nuance}}
\quad\frac{\phantom{i}}{}\quad
\underbrace{\text{Y}\ \underset{\vphantom{|^|}\phi}{90}\ \text{R}}_{\text{hue}}
</math>

with

: <math>w = 100 - c - s = 100 - 30 - 20 = 50</math>

=== Saturation and lightness ===
In addition to the above values ''s'' (blackness), ''w'' (whiteness), ''c'' (chromaticness) and ''Φ'' (hue), the NCS system can also describe the two perceptual quantities [[Colorfulness#Saturation|saturation]] and lightness. NCS saturation (''m'') refers to a color's relation between its chromaticness and whiteness (regardless of hue), defined as the ratio between the chromaticness and the sum of its whiteness and chromaticness <math>m = c / (w + c) = c / (100 - s)</math>. The NCS saturation ranges between 0 and 1.

For the example color of '''S 2030-Y90R''', the saturation is calculated as 
: <math>m = c / (100 - s) = 30 / (100 - 20) = 30 / 80 = 0.375.</math>

NCS lightness (''v'') is a color's perceptual characteristic to contain more of the achromatic elementary colors black or white than another color. NCS lightness values varies from 0 for the elementary color black (S) to 1 for the elementary color white (W). For achromatic colors, that is any black, gray or white with no chromatic component (''c'' = 0), lightness is defined as 
: <math>v = \frac{100 - s}{100}.</math>

For chromatic colors, the NCS lightness is determined by comparing the chromatic color to a reference scale of achromatic colors (''c'' = 0), and is determined to have the same lightness value ''v'' as the sample on the reference scale to which it has the least noticeable edge-to-edge difference.

=== Examples ===
Two examples of NCS color notation&mdash;the yellow and blue shades of the [[Swedish flag]]:<ref>{{Cite web|url=https://lagen.nu/1983:826|title=Swedish legal regulation on flag colour|date=2016-03-29}}</ref>
* {{colorsample|#FFC300|description=sample of 0580Y10R}} Yellow – NCS 0580-Y10R (nuance = 5% blackness, 80% chromaticness, hue = 90% yellow + 10% red. Strong, very slightly blackish yellow with a slight orangish tinge)
* {{colorsample|#015483|description=sample of 4055R95B}} Blue – NCS 4055-R95B (nuance = 40% blackness, 55% chromaticness, hue = 5% red + 95% blue. Somewhat dark, medium strong blue with a very slight purplish tinge)
The NCS is represented in nineteen countries and is the reference norm for color designation in [[Sweden]] (since 1979), [[Norway]] (since 1984), [[Spain]] (since 1994) and [[South Africa]] (since 2004). It is also one of the standards used by the [[International Colour Authority]], a leading publisher of color trend forecasts for the [[interior design]] and textile markets.