Why does Mark Twain emphasize the color of Pap Finn's very white skin in the beginning of Chapter 5?
Twain is foreshadowing Pap Finn's untimely death in the brothel in coming chapters.
Twain is making Pap a symbol for greed. His lack of color shows off his moral decay and covetousness.
Twain is drawing a connection between Pap and the Widow Douglas. Pap's lack of color comes from his lack of religious conviction, while the Widow, who is a deep believer in the the Lord, is not as sickly white as Pap.
Twain is pointing out that alcohol has drained away Pap's color and his humanity.
Twain is drawing a connection between Pap Finn and Jim. Jim is ultimately the better man in the story, as shown by the actions and words of both characters. Twain argues that one cannot judge a person based on skin color.