"She is fantastic," Colleton told TV Guide. "She plays this woman named Hannah, who took off from this small rinky-dink Florida town and ran off with this older guy and they went on this wild killing spree.
"So when they got caught, she turned state's evidence on the boyfriend, he went to jail for life and she started a new life. Years later, she's in her 30s and she will intersect with Dexter. I would say Hannah is a still water that runs very deep and is quite unlike any woman Dexter has ever known."
Colleton added that there is "always the possibility" that a romance could develop between Dexter (Michael C Hall) and Hannah.
"Whenever there's a man and a woman, there's always that possibility - or a man and a man or a woman and a woman or any configuration," she said. "[But] there's nothing needy about Hannah.
"Every woman that Dexter's ever... been involved with have been incredibly needy. Hannah has a cool aloofness, but there's something about her that will intrigue him."
Dexter returns to Showtime on Sunday, September 30 at 9/8c. In the UK, Dexter airs on FX.