Which colors are mixed together results in blue

The mixing of colors is subject to different laws, depending on whether we are dealing with colored light or with colored substances (body colors). The two essential laws of color mixing are those of additive color mixing and subtractive color mixing.

The additive color mixing

When we work with colored light, we are dealing with the law of additive color mixing. Corresponding to the three types of cones in the human retina, it is based on the three primary colors red, green and blue. Mixing creates lighter shades. A mixture of red and green creates yellow, green and blue creates cyan - and blue mixed with red creates magenta. If all three colors come together in full intensity and in the same proportions, they complement each other to form white.
This is the principle on which color television and the display of colors on the computer screen work. In graphics software, we know it as an RGB model (RGB = red, green, blue). It is also sometimes referred to as the physical color model.

The subtractive color mixing

When working with color substances (e.g. when printing) we are dealing with the law of subtractive color mixing. Color substances absorb certain wavelengths of white light while they reflect other wavelengths.
A color substance that absorbs short-wave light (blue) reflects long- and medium-wave light and is therefore perceived by us as yellow. If a color substance absorbs medium-wave light (green), it reflects short-wave and long-wave light and we see magenta. If long-wave light (red) is absorbed by a color substance and short- and medium-wave light is reflected, then we see cyan.

These three basic colors yellow, cyan and magenta are used as a starting point for subtractive color mixing. Mixed color substances absorb several wavelengths of light and reflect mixed tones that are darker than the three primary colors. The luminosity of the colors decreases when they are mixed, which is why this type of color mixing is called subtractive color mixing. A mixture of cyan and magenta creates blue. Magenta mixed with yellow results in red. Yellow mixed with cyan results in green. If you mix cyan, magenta and yellow together in full intensity and in equal proportions, you get black, i.e. no more light is reflected.
Color photography and 3-color printing work according to the principle of subtractive color mixing. In the case of 4-color printing, an intensive black is also used in order to give the print image more depth and so that pure black areas do not have to be mixed from the three basic colors. With graphics software, we know this principle as a CMY or CMYK model (CMYK = cyan, magenta, yellow, black).

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© 2002 Ingrid Crüger, Fraunhofer IPSI