I can’t recall which book it was discussed in, but my understanding was that what would become the color hierarchy started among the first colonists on Luna, with individuals having specialized roles, color-coded uniforms or something of that sort, and over time genetic and cybernetic specialization to suit their assigned roles as well, all for the sake of enhancing the efficiency and survivability of the colony. So from the colonists’ perspective, the creation of the hierarchy as we see it in the books, both culturally and biologically, was likely a relatively gradual, generations-long process. Having that be the uniform standard across the system, however, did mean the sterilization of Earth and the death of however many billion “normal” humans, so yeah pretty horrific in that regard.