The interesting bit is that this even translated to other languages. In Germany the "Gelbe Seiten" (literally yellow pages) was the commercial listings and the "Telefonbuch" (telephone book) was for normal numbers.
I wonder if this is related, specifically the origin and use of the term in the 1890s - it somewhat connects as to why yellow paper was used for advertising, perhaps?
https://en.wikipedia.org/wiki/Yellow_journalism
