Primary colors are hues that can be mixed to produce a wide gamut of colors. There are different sets of primary colors depending on what mixing model you are using. Most of us are familiar with the red, yellow, and blue (RYB) primaries, which is taught to children when they are acquiring basic art skills. These are still the primaries that most painters, artists, and interior designers use today. The RYB model is an example of a subtractive color model. Subtractive mixing is when inks, colorants, or pigments form new colors by absorbing some parts of the visible spectrum. Cyan, magenta, and yellow (CMY) are also subtractive primaries. Typically used in color printing, traditional red and blue were substituted with magenta and cyan over time as technology advanced and these pigments allowed for a wider range of colors. CMYK is also the name for the printing process itself, with the K standing for “key ink.” This is typically a black that helps pull out artistic detail, as the black achieved by mixing the three primaries is more grey. The last model used is the red, green, and blue (RGB) system. RGB is an additive color model, which begins with darkness and uses different colors of light mixed together to achieve white. We most commonly see this model on computer and television screens. Photographers will also be quite familiar with working with an RGB color profile when editing images to be used online and switching over to a CMYK color profile when printing.
Source: Jessica Stewart on October 5, 2018 "Learn How Color Theory Can Push Your Creativity to the Next Level"