My female Jackson tends to always hang out on the top-most vine in her enclosure despite her having about a dozen other sticks and a pothos and an umbrella tree to climb on, and she's been fine. Maybe they just like being at the highest point?
As far as your girl's colors, I don't really have an answer. My female Jackson tends to only turn a light shade of green when she's sleeping or in her outdoor enclosure. If she's inside she tends to be a darker, almost forest green color, even when basking. She is only brown when she's really stressed or angry, like when I recently added a new plant to her enclosure she was really aggravated by the addition and was a brownish color for a few hours.