<P> Isaac Newton introduced indigo as one of the seven base colors of his work . In the mid-1660s , when Newton bought a pair of prisms at a fair near Cambridge , the East India Company had begun importing indigo dye into England , supplanting the homegrown woad as source of blue dye . In a pivotal experiment in the history of optics , the young Newton shone a narrow beam of sunlight through a prism to produce a rainbow - like band of colors on the wall . In describing this optical spectrum , Newton acknowledged that the spectrum had a continuum of colors , but named seven : `` The originall or primary colours are Red , yellow , Green , Blew , & a violet purple ; together with Orang , Indico , & an indefinite varietie of intermediate gradations . '' He linked the seven prismatic colors to the seven notes of a western major scale , as shown in his color wheel , with orange and indigo as the semitones . Having decided upon seven colors , he asked a friend to repeatedly divide up the spectrum that was projected from the prism onto the wall : </P>
<P> Isaac Newton introduced indigo as one of the seven base colors of his work . In the mid-1660s , when Newton bought a pair of prisms at a fair near Cambridge , the East India Company had begun importing indigo dye into England , supplanting the homegrown woad as source of blue dye . In a pivotal experiment in the history of optics , the young Newton shone a narrow beam of sunlight through a prism to produce a rainbow - like band of colors on the wall . In describing this optical spectrum , Newton acknowledged that the spectrum had a continuum of colors , but named seven : `` The originall or primary colours are Red , yellow , Green , Blew , & a violet purple ; together with Orang , Indico , & an indefinite varietie of intermediate gradations . '' He linked the seven prismatic colors to the seven notes of a western major scale , as shown in his color wheel , with orange and indigo as the semitones . Having decided upon seven colors , he asked a friend to repeatedly divide up the spectrum that was projected from the prism onto the wall : </P>
when did indigo become a color of the rainbow
when did indigo become a color of the rainbow
In the mid-1660s
In the mid-1660s