Pierce Brown assigned the colours to the castes mainly by basing them off of the hierarchy that Plato put forth in his Republic.[Official 1] In Book VI, Plato names three main groups that would make up his Polis: Hoi Polloi, the many producers (corresponds with the lowColors) with souls of iron or bronze, Hoi Epikouroi, auxiliaries which are militant forces and so on (corresponding with the midColors) with souls of silver, and Hoi Phylakes which would be the ruling class, like the highColors, with souls of gold. However, the Guardians must breed to produce superior stock (an oft-used word in the series) but be kept unwares of this with the "Noble Lie." Furthermore, Plato asserts that each member of the aristocratic state should only perform one kind of work, further revealing the influence of the text on the Society that Brown created.
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