In Bret Harte's "The Outcasts of Poker Flats," one of the main characters in the story is the Duchess, who is a prostitute. She is one of the several "undesirable" people who have been exiled from the town.
In the paragraph in question, Piney, the young, naive and loving (and lovable) fiancée of Simson has made the statement regarding the living conditions they now find themselves in. Without knowledge of the Duchess' profession, Piney notes that their humble surroundings may not be as nice as those the Duchess enjoyed in Poker Flats. This is a stark reminder to the Duchess as to why she is no longer in Poker Flats. It is embarrassing to her, especially coming from Piney, who the Duchess comes to care for very much.
"I reckon now you're used to fine things at Poker Flat," said Piney. The Duchess turned away sharply to conceal something that reddened her cheeks through its professional tint, and Mother Shipton requested Piney not to "chatter."
The "professional tint" the author uses to refer to the Duchess' color of face is the makeup she wears because of her profession, as opposed to her heightened color when she blushes naturally, as she does with embarrassment at Piney's innocent comment.