There a distinctive difference between color-sorted and color-coded libraries. However, the second may be a subset of the first. But in any case, we'd like to talk about libraries sorted by the colors of their books' covers today.
Those living at the end of the 19th and beginning of the 20th century saw library books in a different light than us. For many, library books had the potential to transmit some of the most infectious diseases circulating in society at the time.