"A damp streak of hair lay like a dash of blue paint across her cheek, and her hand was wet with glistening drops as I took it to help her from the car." In this quote from The Great Gatsby, is there any significance to the word "damp"? Also, the symbolism of blue makes sense, but why "paint"? Is this because it washes away—its stain temporary?

This quote, which appears in chapter 5 of The Great Gatsby, describes Daisy Buchanan as she arrives at Nick Carraway's house to visit with him and Gatsby. Daisy's hair is described as damp because she is coming in out of the rain. This is significant because of the way weather functions as metaphor throughout this chapter: when Daisy arrives, the rain stops, but when she leaves, it starts up again. The rain mirrors Gatsby's emotional state, first anxious and melancholy as he waits for Daisy's arrival and worries that things will not be as they once were between them, then happy while Daisy is with him, and finally crushed when she leaves again. The dampness of Daisy's hair also serves to explain why it's sticking to her face at all when she is usually so put together.
Throughout the novel, Daisy is associated with the color blue, emphasizing both her sadness and her status as a "blue blood," and her description here continues this trend. Your hazard that using paint as a metaphor is meant to draw attention to the fleeting, temporary nature of Daisy and Gatsby's relationship, and this visit in particular, is a fair one. The description could also be playing with the idea of paint as makeup. Daisy is very much concerned with appearances and with performing a part. In this scene, coming out of the rain and opening up with Gatsby, she is far less put together than usual, and it might be tempting to think she has her mask off, but the description of even her messy hair as "paint" may imply otherwise.