Purple
Optics

The meanings of the color terms violet and purple varies even among native speakers of English, for example between United Kingdom and United States. Optics research on purple and violet contains contributions of authors from different countries and different native languages, it is likely to be inconsistent in the use and meaning of the two colors.

According to some speakers/authors of English, purple, unlike violet, is not one of the colors of the visible spectrum. It was not one of the colors of the rainbow identified by Isaac Newton. According to some authors, purple does not have its own wavelength of light. For this reason, it is sometimes called a non-spectral color. It exists in culture and art, but not, in the same way that violet does, in optics. According to some speakers of English, purple is simply a combination, in various proportions, of two primary colors, red and blue. According to other speakers of English, the same range of colors is called violet.

In some textbooks of color theory, and depending on the geographical-cultural origin of the author, a "purple" is defined as any non-spectral color between violet and red (excluding violet and red themselves). In that case, the spectral colors violet and indigo would not be shades of purple. For other speakers of English, these colors are shades of purple.

In the traditional color wheel long used by painters, purple is placed between crimson and violet. However, also here there is much variation in color terminology depending on cultural background of the painters and authors, and sometimes the term violet is used and placed in between red and blue on the traditional color wheel. In a slightly different variation, on the color wheel, purple is placed between magenta and violet. This shade is sometimes called electric purple (see shades of purple).

In the RGB color model, named for the colors red, green, and blue, used to create all the colors on a computer screen or television, the range of purples is created by mixing red and blue light of different intensities on a black screen. The standard HTML color purple is created by red and blue light of equal intensity, at a brightness that is halfway between full power and darkness.

In color printing, purple is sometimes represented by the color magenta, or sometimes by mixing magenta with red or blue. It can also be created by mixing just red and blue alone, but in that case the purple is less bright, with lowersaturation or intensity. A less bright purple can also be created with light or paint by adding a certain quantity of the third primary color (green for light or yellow for pigment).
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