It is true that Hurston employs a dialect that is specific to black Floridians, as well as certain colloquialisms, or phrases used in ordinary speech, that were also particular to this group of people at this time. Consider the following exchange between Hicks and Coker:
"It takes money tuh feed pretty women. Dey gits uh lavish uh talk."
"Not lak mine. Dey loves to hear me talk because dey can't understand it. Mah co-talkin' is too deep. Too much co to it" (34).
Notice the ungrammatical usage of "lavish" and "talk" in the second sentence as well as Hurston's inclusions of the pause, "uh." Hicks uses the expression "co-talkin'" which is an example of one of the many colloquialisms used in the novel. He is also playful with this language ("[t]oo much co to it").
If you read the exchange between Hicks and Coker on this page, you will notice that Hurston does not always designate the speaker. This form of dialogue is found in other novels of the time, especially those written by Ernest Hemingway. This tendency to continue the dialogue, without the narrator interrupting to let us know who is speaking, is a common feature of Modernist literature.
Another common aspect of Modernist literature is the use of free-indirect discourse, which is found here as well. She employs what Henry Louis Gates, Jr., refers to as a "double voice," echoing W.E.B. DuBois's concept of "double-consciousness." According to Gates, Hurston can assume the voices of her less educated, rural subjects, then, when narrating, employ her highly literate, cosmopolitan voice. She moves seamlessly in and out of each, showing, as many black Americans do, how they are able to employ mainstream standards of speech while also maintaining their own modes of speech, which are no less rich or descriptive.
Source: Hurston, Zora Neale. Their Eyes Were Watching God: A Novel. New York: Harper Perennial, 1990. Print.