There is a hardly manageable number of different approaches to cataloging colors, according to very different criteria and for different purposes. In art and science, it was initially about a fundamental interest in how our subjective and intersubjective perception of color comes about; in fashion and design, it was later about harmonious color chords and their reliable reproduction.
For industry, it was ultimately necessary to ensure that one and the same color tone could be mixed identically again and again - for this reason, systems were developed that mathematically coded certain farm tones for the first time. For printing, mainly on paper and textiles, the nature of the substrate also played a role.
For physical reasons, but also partly simply because of trademark protection, it is not always possible to merge color systems arbitrarily.
The following is a brief overview of a small selection of the most important color systems.
Color theory according to Newton, Goethe, Itten
Isaac Newton discovered in the 17th century that a ray of light, directed through a prism onto a white surface in a dark room, splits into a spectrum of all the colors of the rainbow, and thus came closer to the realization that white daylight is composed of light rays of different frequencies, which the human perceptual apparatus translates into the subjective impression of different colors. At the same time, Newton made a division of the spectrum into seven categories, parallel to the tones of a musical scale.
In the late 18th century,Johann Wolfgang von Goethe developed a color theory that already contained the idea of primary colors, which served as the basis for the representation of the other colors. He assumed that yellow originated from light, blue from darkness, and all other colors as a mixture of these two; as a second complementary pair, he added purple and green on the basis of retinal afterimage effects to finally complete the circle with orange and violet. Although his system was not sustainable in the long run, it at least still enjoys great anecdotal popularity today.
In the 1920s, Bauhaus professor Johannes Itten developed a color model designed for art education that shows how three secondary colors (green, orange, purple) can be mixed from three primary colors (red, yellow, blue). Each primary color has a complementary secondary color; in between there are also tertiary mixed colors.
The system has the disadvantage that the mixing of complementary colors does not result in a pure gray, as it theoretically should, but in various brownish tones. Nevertheless, it became the basis for knowledge about subtractive color mixing, on which today, for example, the CMYK model is based, and it is still taught in schools today because of its ease of communication.
Color systems NCS and RAL
RAL and NCS colors are opaque and thus independent of their respective carrier material; they are two early attempts to systematize surface colors mathematically in such a way that no physical color sample is absolutely necessary for transmission, but a code can be communicated that allows the same color tone to be achieved across industries.
Between 1937 and 1939, the Swedish physicist Tryggve Johansson developed an NCS coding system in a series of laboratory experiments that assigned color tones a key consisting of numbers and letters according to four criteria: saturation; white content; black content; position in a matrix of the four primary colors red, yellow, green and blue. Their exact tone was determined by surveys in which subjects were asked to indicate the tone they perceived as purest - for example, the purest yellow, without any admixture of green or red. In this way, subjective human perception was empirically incorporated into the development of the canon. The catalog based on this has existed in its final form since 1979 and has only been updated in subsequent years by adding further intermediate shades. The NCS coding is used for so-called surface colors, i.e. for mixing paints and varnishes, but cannot be completely converted into CMYK and RGB tones.
The RAL color system existed in its first form in Germany from 1927 and was chronologically the first to code color shades in such a way that they could always be mixed identically. It was first used in painting and varnishing, and later, with a parallel set, in design and advertising, as well as in a third set for plastics. Many "official" color tones, i.e. the exact tones of the police, state or state-related organizations in the German-speaking countries such as railroads, postal service, fire department and THW, camouflage and uniform colors of the German armed forces and many more are coded by RAL. The transfer into sRGB is possible under certain conditions, so that on calibrated screens the respective tones can be approximately represented.
In today's "Digital World
The American company Pantone set itself the task of systematizing color tones for printing with the aid of a numerical model in such a way that each color can be replicated without error depending on the printed material. Even tones that are not covered by the CMYK system, such as gold and silver tones, are included in the Pantone system. It consists of 18 basic colors and their lightenings or darkenings, as well as some additional spot colors.
HKS was developed for printing primarily on paper and provides several parallel compartments adapted to the material to be printed, so that each tone can be replicated objectively - independently of human perception - on different materials.
Colors by reflecting light from surfaces: CMYK is a subtractive mixing system designed for printing in which ink dots of only four colors can be superimposed on a white background to form any tone. The components are cyan blue, magenta, yellow and black (called "key" in the CMYK system). Metallic tones, for example, cannot be reproduced in this way; these must be created separately for printing.
Colors from direct light sources: The RGB system is used for true-color viewing on calibrated screens and is based on additive color mixing, i.e. the superimposition of two light colors to form a brighter one. The starting point is the three primary colors red, green, and blue, whose superposition results in yellow, cyan, and magenta; the superposition of all three results in white, their absence in black, and all intermediate shades are achieved by dimming the light intensity of the respective color in one point. Any digital image can be converted - approximately - from RGB to CMYK and vice versa, depending on whether it is to appear in print or on a website / in a digital document.