Colors, sort colors, main colors, color standards like: CMYK, RGB system, pantone colors and the RAL numbers. What are colors anyway? An explanation

Spectrum of colors

Color is the visual perceptual property of humans that can category the main colors like: red, green, blue and the and all the colors between any of these main colors. The variety of colors is called the spectrum of light. This is a distribution of light energy versus wavelength. These are interacting with the eye that send these receptors to are brain to recognize the various colors. Color categories and physical specifications of color are also associated with objects, materials and light sources like the sun or a bulb, based on their physical properties such as light absorption, reflection, or emission spectra. We speak of a color space where colors can be identified numerically by their coordinates.

The main colors
The main colors are: white, green, blue, yellow and red. Every other color can be made by mixing 2 are more main colors. You get black if you mix the green, blue, yellow and red color true each other.

RGB-system (Red, Green, Blue)
Mostly made for displaying film on television and computer screens. The 3 colors (Red, Green, Blue) can be overlapped with each other to create other colors.

CMYK-system (Cyan, Magenta, Yellow, Key (Black))
Is an 4 based system including the black color. This system is made for printing with inkjet-printers.

Pantone-system
Pantone is a company that published a color-code. This code is made to have color-standards in exchange with other companies. The first serie has 500 colors numbered from PMS 100. Later they added the fluorescent colors.

RAL-system
RAL is a color matching system used in Europe. In colloquial speech RAL refers to the RAL CLASSIC system, mainly used for varnish and powder coating.
In 1927 the German Reichsausschuß für Lieferbedingungen und Gütesicherung" (State Commission for Delivery Terms and Quality Assurance) invented a collection of 40 colors under the name of "RAL 840". Prior to that date manufacturers and customers had to exchange samples to describe a tint, whereas from then on they would rely on numbers.
In the 1930s the numbers were changed uniformly to four digits and the collection was renamed to "RAL 840 R" (R for revised). With tints constantly added to the collection, it was revised again in 1961 and changed to "RAL 840-HR", which consists of 210 colors and is in use to this day. In the 1960s the colors were given supplemental names to avoid confusion in case of transposed digits.
As "RAL 840-HR" covered only matte paint the 1980s saw the invention of "RAL 841-GL" for glossy surfaces, limited to 193 colors. A main criteria for colors in the RAL CLASSIC collection is to be of "paramount interest". Therefore most of the colors in it are used on warning and traffic signs or are dedicated to government agencies and public services (for example: RAL 1004 - Swiss Postal Service, RAL 1021 - Austrian Postal Service, RAL 1032 - German Postal Service).

The first digit relates to the shade of the color:
1xxx Yellow RAL 1000 Green Beige - RAL 1034 Pastel Yellow (27)
2xxx Orange RAL 2000 Yellow Orange - RAL 2012 Salmon Orange (12)
3xxx Red RAL 3000 Flame Red - RAL 3031 Orient Red (22)
4xxx Violet RAL 4001 Red Lilac - RAL 4010 Telemagenta (10)
5xxx Blue RAL 5000 Violet Blue - RAL 5024 Pastel Blue (23)
6xxx Green RAL 6000 Patina Green - RAL 6034 Pastel Turquoise (32)
7xxx Grey RAL 7000 Squirrel Grey - RAL 7047 Telegrey 4 (37)
8xxx Brown RAL 8000 Green Brown - RAL 8028 Terra Brown (19)
9xxx White/Black RAL 9001 Cream - RAL 9018 Papyrus White (12)

Sources: Wikipedia and mostly own knowledge