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A rainbow spans a continuous spectrum of colors; the distinct bands are an artifact of human color vision. In Roy G. Biv, the colors are arranged in the order of decreasing wavelengths, with red being 650 nm and violet being about 400 nm. The Roy G. Biv arrangement is memorable because Roy is a common male given name, forming the acronym into a first name, middle initial, and a last name.
In Classical Antiquity, Aristotle claimed there was a fundamental scale of seven basic colors. In the Renaissance, several artists tried to establish a new sequence of up to seven primary colors from which all other colors could be mixed. In line with this artistic tradition, Newton divided his color circle, which he constructed to explain additive color mixing, into seven colors. His color sequence including the tertiary color indigo is kept alive today by the Roy G. Biv mnemonic. Originally he used only five colors, but later he added orange and indigo, in order to match the number of musical notes in the major scale.
The Munsell color system, the first formal color notation system (1905), names only five "principal hues": red, yellow, green, blue, and purple (although note that Munsell's purple is not a spectral hue).
Another traditional mnemonic device has been to turn the initial letters of seven spectral colors into a sentence. In Britain the most common is "Richard Of York Gave Battle In Vain." The mnemonic is said to refer to the defeat and death of Richard, Duke of York at the Battle of Wakefield. In order to avoid reference to this defeat, people from Yorkshire developed the alternative "Rowntrees Of York Gave Best In Value." Alternatively, the biblically inspired "Read Out Your Good Book In Verse," or the more anarchic "Rinse Out Your Granny's Boots In Vinegar," may be used.