The Great Gatsby, "in trembling opale

Could you please tell me the meaning of "in" in the following excerpt from The Great Gatsby, chapter 2? Does it mean "dressed in" "wearing"? And how do you interpret this metaphor?

Suddenly one of the gypsies in trembling opal seizes a cocktail out of the air, dumps it down for courage and, moving her hands like Frisco dances out alone

on the canvas platform.

Thank you.