Arguably the question is asking you to analyze the contrast between how individuals act behind closed doors, and how they appear in the presence of society. It is all part of the assumed masquerading in which all adult individuals indulge to hide the darkest and least likable traits of their personality.
Check out how the character of Blanche is first introduced in scene one.
Her appearance is Incongruous to this setting. She is daintily dressed in a white suit With a fluffy bodice, necklace and earrings of pearl, white gloves and hat, looking as if she were arriving at a summer tea or cocktail party in the garden district.
Here is a combination of character traits that are juxtaposed with the setting, making them "incongruous." This is because Blanche, as her name symbolically suggests, is characterized by purity, a sense of innocence, and a child-like, yet coquettish, disposition. However, beneath the imagery produced by those fancy, fluffy clothes, hides a woman nearly broken, one with a murky past, questionable intentions, and a lost sense of self. She is the exact opposite of what her social mask shows.
Judging from the stage directions, you can almost feel that those who witness Blanche's arrival are not buying her social costume, either. They do not change their demeanor to try to mimic what would have been a social "superior." They do not even feel intimidated by her. It is as if Blanche was exactly in her element among the dusty, dirty and shady territory. The only difference is that she is dressed to play a different part.
Further evidence of the public not buying Blanche's outfit is also stated in the stage directions, where the narrator semi-sarcastically points out that this "done up" woman comes with certain conditions.
She is about five years older than Stella. Her delicate beauty must avoid a strong light. There is something about her uncertain manner, as well as her white clothes, that suggests a moth.
A comparison to a butterfly could have sounded more favorable. This shows the limited redeeming qualities that could have turned her into a much better person, a butterfly. Blanche's beauty and looks are merely skin deep. She hides her individual reality from society, but fails at convincing them that she is something other than ordinary.