Why do you think Charles Chestnutt focuses so much on skin color as the backdrop for "The Wife of His Youth"?
"The Wife of His Youth" is the best-known story in Charles Chestnutt's collection regarding the "color line." Of course, legal segregation had drawn a line, separating the lives of black and white people. However, there was also "a line" that was intended to separate light-skinned blacks from dark-skinned ones. It is this distinction on which Chestnutt focuses in the story.
Mr. Ryder, the protagonist, is organizing a ball. He is also known to be "the dean of the Blue Vein Society," an organization of well-to-do light-skinned blacks in some Northern cities. The Blue Vein Society was a real organization. Only black people whose skin was light enough so that their veins were transparent through the skin were allowed into the club. There were other similar social tests to determine one's fitness, such as the "paper bag test." For this one, a standard paper bag was placed over someone's head. If their skin was the same color or lighter than the bag, then they would be granted entry into the society.
During Chestnutt's time, the late-19th and early-20th century, having light skin was associated with being more refined, more educated, and having better manners. In the story, Mr. Ryder is said to have "irreproachable" manners and "poetry was his passion." These aspects of his character, in addition to his ability to throw a ball, indicate that he has had certain opportunities that have been denied to other black people. Moreover, light skin was prized for its proximity to whiteness. Mr. Ryder is said to have "refined" features and "his hair was almost straight." "Refined" features usually indicated European features: an aquiline nose and thin lips. Having these features often allowed people who would have been considered black to "pass" for white.
Later in the story, a darker-skinned black woman comes knocking at Mr. Ryder's door, inquiring as to the whereabouts of her husband, Sam, who turns out to be Mr. Ryder. She is inarticulate and uneducated. We learn that they were married during slavery. She had been sold away, soon after his escape North.
Chestnutt's story ends happily, in that Mr. Ryder and his guests agree to "acknowledge" this woman. Acknowledgement here works in two senses: he acknowledges that this is his wife; she is also acknowledged as a member of their society -- one of their people -- in spite of rules that would disqualify her on the basis of skin color. With this final comment, Chestnutt is saying that the standards of societies such as the Blue Veins are wrong, and that black people are one people who should acknowledge and accept one another, disavowing colorism, or discrimination amongst people of the same race or ethnicity on the basis of skin color.
In this short story, as in numerous others by Chestnutt, skin color is not a "backdrop," but is instead a major theme. His stories examine the ways in which black people had been affected by racism, internalizing white people's beliefs about the inferiority of blackness.