of Deep Purple which formed in 1968. Later, in the 1980s, it was featured in the song and album Purple Rain (1984) by the American musician Prince. The Purple Rain Protest was a protest against apartheid that took place in Cape Town, South Africa on 2 September 1989, in which a police water cannon with purple dye sprayed thousands of demonstrators. This led to the slogan The Purple Shall Govern. The violet or purple necktie became very popular at the end of the first decade of the 21st century, particularly among political and business leaders. It combined the assertiveness and confidence of a red necktie with the sense of peace and cooperation of a blue necktie, and it went well with the blue business suit worn by most national and corporate leaders. In science and nature 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 Since this Wikipedia page contains contributions from authors from different countries and different native languages, it is likely to be not consistent in the use of the color terms violet and purple. 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, although in earlier versions of Newton's work the word purple was used where violet was used in the final version. 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). The spectral colors violet and indigo would in that case not be purples. For other speakers of English, these colors are purples. 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