Opticks: or, a Treatise of the Reflexions, Refractions, Inflexions and Colours of Light

Opticks is Isaac Newton's own treatise on light, first published in 1704, cited here from the Gutenberg edition of the historical English text, and Book One, Part Two, is where Newton lays out his division of the visible spectrum into seven named colours along with his explicit analogy between those seven colour intervals and the seven intervals of the musical octave. As Newton's own primary presentation of an idea that shaped centuries of subsequent color theory, it is the correct source for what he actually argued and how he framed the color music analogy himself, tiered here the same way the atlas tiers other historical primary sources such as Pliny, Dioscorides and Agrippa. Its limit is that it presents seventeenth century natural philosophy in its own terms, so a claim about modern optics or color science needs a current scientific source rather than Newton's own historical text.