The "The Outcasts of Poker Flats," what does Harte mean by "professional tint," and why is it considered "professional?"

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.