What could the color green represent when Esperanza tells us her “dress was green” after she tries to die?

In the novel The House on Mango Street, the chapter (or vignette) that references Esperanza's green dress is entitled "The Monkey Garden." In this vignette, Esperanza begins by describing a family from Kentucky that had a monkey they kept in a green metal cage. When the family moved away, the kids in the neighborhood began going into the family's garden, which they were afraid to go into when the monkey lived there, because he would scream and bare his teeth. Esperanza still wants to be a kid and play games using her imagination. Sally is more interested in boys than in childish games.

In the preceding vignette, entitled "What Sally Said," Sally's father is beating her, and she comes to stay with Esperanza's family. But her father shows up and apologizes, and Sally goes with him. The vignette ends with Sally being beaten again and not coming to school for days.

In "The Monkey Garden," Esperanza doesn't understand that the boys are not truly taking advantage of Sally. They take her keys and tell her she has to kiss them before they give the keys back to her. Esperanza is angry at the injustice of this and tries to do something, but she doesn't understand that Sally is a willing participant in their game. 

"I don't know why, but something inside me wanted to throw a stick. Something wanted to say no when I watched Sally going into the garden with Tito's buddies all grinning. It was just a kiss, that's all. A kiss for each one. So what, she said. Only how come I felt angry inside. Like something wasn't right."

Esperanza runs to Tito's mother's house and tells them the boys won't give Sally her keys. Tito's mother doesn't do anything and barely looks up from her ironing. Esperanza then picks up sticks and a brick with the intention of going back to the garden to defend Sally. The boys and Sally tell her to go home and look at her like she's stupid and childish. She feels so ashamed that she runs to the other end of the garden, which she describes as "the jungle part," to hide. She gets on the ground and cries. She wants to die from embarrassment and shame. When she gets up, she says her dress is green. She doesn't tell us what color her dress was, but it may have been white. She was wearing white socks. 

Regardless of what color her dress was, it's surely been stained green by foliage and grass. This is a reference to the monkey's green cage. Because of her actions, and the fact that she didn't understand that Sally wasn't truly in danger, Esperanza feels as foolish as the monkey who used to live in the green cage in the garden.