Some body explain this to me what it means i got this from the Great
Gatsby by F. Scott Fitzgerald in Chapter-3

?You've dyed your hair since then,? remarked Jordan, and I started,
but the girls had moved casually on and her remark was addressed to
the premature moon, produced like the supper, no doubt, out of a
caterer's basket.

This passage is Fitzgerald's way of indicating the frivolous and
tactless quality of a certain affluent young woman's mind.

When a girl whom Jordan Baker barely knows shows up at a gathering at
Jay Gatsby's house and says "We met you here about a month ago,"
Jordan makes the casual and rather rude comment "You've dyed your hair
since then," which astonishes Nick Carraway, the first-person narrator
of the novel. Jordan isn't really expecting an answer or observation
in response, and she doesn't receive one; the conversation moves on in
a casual fashion. Jordan is talking to no one in particular, as if she
were speaking to the moon. She has plucked the remark out of her head
as one might pull a loaf of bread or a bottle of wine out of a picnic
hamper or a caterer's food basket.

Jordan Baker is not portrayed in a very flattering light. Earlier in
the novel, this is said of her (by the narrator, Nick Carraway):

"I knew now why her face was familiar--its pleasing contemptuous
expression had looked out at me from many rotogravure pictures of the
sporting life at Asheville and Hot Springs and Palm Beach. I had heard
some story of her too, a critical, unpleasant story, but what it was I
had forgotten long ago."

I hope this helps! If anything is unclear, please request
clarification; I'll be glad to offer further assistance with this
question before you rate my answer.

Best regards,
pinkfreud