The term color line was originally used as a reference to the racial segregation that existed in the United States after the abolition of slavery. An article by Frederick Douglass titled "The Color Line" was published in the North American Review in 1881. The phrase gained fame after W. E. B. Du Bois’ repeated use of it in his book The Souls of Black Folk.
It is difficult to find an exact origin of the phrase "the color line". In 1881 Frederick Douglass published an article with that title in the North American Review.
At the First Pan-African Conference in London in July 1900, the delegates adopted an "Address to the Nations of the World", drafted by Du Bois and to which he was a signatory, that contained the sentence: "The problem of the Twentieth Century is the problem of the colour-line".
Three years later, in his 1903 book, Du Bois used the phrase first in his introduction, titled "The Forethought", writing: "This meaning is not without interest to you, Gentle Reader; for the problem of the Twentieth Century is the problem of color line". The phrase occurs again in the book's second essay, "Of the Dawn of Freedom", at both its beginning and its end. At the outset of the essay, Du Bois writes: "The problem of the twentieth century is the problem of the color-line—the relation of the darker to the lighter races of men in Asia and Africa, in America and the islands of the sea". At the end of the essay, Du Bois truncates his statement to: "The problem of the twentieth century is the problem of the color-line", the more frequently quoted version of the sentiment.
Ample nuance exists among the three versions of Du Bois’ prediction, as within a very short amount of text Du Bois provides the reader with three incarnations of the thought. Some of the difference may be the result of the original serialization of the work, as parts of The Souls of Black Folk were originally serialized, many in The Atlantic Monthly. The first reference draws the reader in with a direct reference, while the second goes so far as to identify all of the areas in the world where Du Bois believed the color-line was "the problem of the twentieth century". All imply, whether directly or passively, that the color-line extends outside the bounds of the United States.
Both the quote and the phrase can be found in numerous texts of the last century, both academic and non-academic alike. Langston Hughes uses the phrase in his autobiography, writing: "In Cleveland, a liberal city, the color-line began to be drawn tighter and tighter. Theaters and restaurants in the downtown area began to refuse to accommodate colored people. Landlords doubled and tripled their rent at the approach of a dark tenant." Closer to the end of the twentieth century, Karla F.C. Holloway, a professor of English at Duke University, centered her keynote address to the National Conference of Researchers of English on this sentence, saying: "Perhaps while sitting in his den or maybe in the midst of academic clutter at his university office, Du Bois penned the epic words that will center my reflections in this essay – 'The problem of the twentieth century is the problem of the color line.'"