Because the spectrum is a continuum, the selecting or omitting of individual colors in a list of representative colors is arbitrary. The traditional inclusion of the color indigo is attributed to Isaac Newton, who wanted the number of colors in his spectrum to come out to seven to match the number of days in the week, the number of notes in the major scale, and the number of known planets. He originally (1672) named only five primary colors: red, yellow, green, blue and violet; only later did he introduce orange and indigo. The Munsell color system, the first formal color notation system (1905), names only five "principal hues": red, yellow, green, blue and purple (though note that Munsell's purple is not a spectral hue).
The meaningless but speakable word ROYGBIV is also used as a mnemonic for the spectral colors, as is its slightly less euphonious reverse VIBGYOR.
Another traditional mnemonic device has been to turn the seven initial letters of the spectral colors into a sentence. In England probably the best known of these 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, a battle which Richard had himself started and which led to the defeat of his forces and his death as well as that of his son.
In Portuguese, this mnemonic is said VLAVAAV (Vermelho, Laranja, Amarelo, Verde, Azul, Anil e Violeta) or VAAVAAV (Vermelho, Alaranjado, Amarelo, Verde, Azul, Anil e Violeta).
In Norwegian, this mnemonic is said ROGGBIF (Rød, Oransje, Gul, Grønn, Blå, Indigo, Fiolet).
In Swedish, this mnemonic is said ROGGBIV (Röd, Orange, Gul, Grön, Blå, Indigo, Violett).
In German, this mnemonic is said ROGGBIL (Rot, Orange, Gelb, Grün, Blau, Indigo, Lila).
In Russian, this mnemonic is said КОЖЗГСФ - Каждый охотник желает знать где сидит фазан (Красный, Оранжевый, Желтый, Зеленый, Голубой, Синий, Фиолетовый).
In Dutch, this mnemonic is said ROGGBIV or Roddelen Over Gekke Grote Broer Is Vals (Rood, Oranje, Geel, Groen, Blauw, Indigo, Violet).
In Indonesian, this mnemonic is said mejikuhibiniu (MErah JIngga KUning HIjau BIru NIla Ungu).