Editing RGB color model (section)

==Additive colors==
[[File:RGB combination on wall.png|thumb|left|Additive color mixing: projecting [[primary color]] lights on a white surface shows secondary colors where two overlap; the combination of all three primaries in equal intensities makes white.]]
To form a color with RGB, three light beams (one red, one green, and one blue) must be superimposed (for example by emission from a black screen or by reflection from a white screen). Each of the three beams is called a ''component'' of that color, and each of them can have an arbitrary intensity, from fully off to fully on, in the mixture.

The RGB color model is ''additive'' in the sense that if light beams of differing color (frequency) are superposed in space their light spectra adds up, wavelength for wavelength, to make up a resulting, total spectrum.<ref>{{cite book | title = Digital Video and HDTV: Algorithms and Interfaces | author = Charles A. Poynton | publisher = Morgan Kaufmann | year = 2003 | isbn = 1-55860-792-7 | url = https://books.google.com/books?id=ra1lcAwgvq4C&q=wavelength+beams+additive&pg=RA1-PA234 }}</ref><ref>{{cite book | title = Lightwave 3d 7.5 Lighting | author = Nicholas Boughen | publisher = Wordware Publishing, Inc | year = 2003 | isbn = 1-55622-354-4 | url = https://books.google.com/books?id=Xsq4JiSssMoC&q=additive-color&pg=PA216 }}</ref>{{anchor|vs-subtractive}} This is in contrast to the [[subtractive color]] model, particularly the [[CMYK color model#CMY|CMY Color Model]], which applies to paints, inks, dyes and other substances whose color depends on ''reflecting'' certain components (frequencies) of the light under which we see them.

In the additive model, if the resulting spectrum, e.g. of superposing three colors, is flat, white color is perceived by the human eye upon direct incidence on the retina. This is in stark contrast to the subtractive model, where the perceived resulting spectrum is what reflecting surfaces, such as [[dye|dyed]] surfaces, emit. A dye filters out all colors but its own; two blended dyes filter out all colors but the common color component between them, e.g. green as the common component between yellow and cyan, red as the common component between magenta and yellow, and blue-violet as the common component between magenta and cyan. There is no common color component among magenta, cyan and yellow, thus rendering a spectrum of zero intensity: [[black]].

Zero intensity for each component gives the darkest color (no light, considered the ''black''), and full intensity of each gives a [[white]]; the ''quality'' of this white depends on the nature of the primary light sources, but if they are properly balanced, the result is a neutral white matching the system's [[white point]]. When the intensities for all the components are the same, the result is a shade of [[gray]], darker, or lighter depending on the intensity. When the intensities are different, the result is a colorized [[hue]], more or less [[Saturation (color theory)|saturated]] depending on the difference of the strongest and weakest of the intensities of the primary colors employed.

When one of the components has the strongest intensity, the color is a hue near this primary color (red-ish, green-ish, or blue-ish), and when two components have the same strongest intensity, then the color is a hue of a [[secondary color]] (a shade of [[cyan]], [[magenta]], or [[yellow]]). A secondary color is formed by the sum of two primary colors of equal intensity: cyan is green+blue, magenta is blue+red, and yellow is red+green. Every secondary color is the complement of one primary color: cyan complements red, magenta complements green, and yellow complements blue. When all the primary colors are mixed in equal intensities, the result is white.

The RGB [[color model]] itself does not define what is meant by ''red'', ''green'', and ''blue'' colorimetrically, and so the results of mixing them are not specified as absolute, but relative to the primary colors. When the exact [[chromaticity|chromaticities]] of the red, green, and blue primaries are defined, the color model then becomes an [[absolute color space]], such as [[sRGB]] or [[Adobe RGB color space|Adobe RGB]].