What about mosaic tile? Lots of colors, styles, sizes, and finishes to choose from. You can also mix tiles or keep it simple and uniform - whatever you prefer! This fireplace was done in a single color of iridescent tiles, very sleek and modern! (other colors available!)

You need light and bright. Being rented is tough. First change out the drapes with to the floor length. Cream with a horizontal stripe of brown to match or furniture. This will 1. get rid of the horrid things hanging there 2. pull the initial visual to that wall instead of the floor. Tall and high colors ( mango, aqua, yellow) decorations on your mantel with shorter cream and brown items. Then a large square table in the middle, painted distressed cream, with high color items setting on it. DIY project or Ikea. Green is the number one calming color, just don't let it put you to sleep. :)

Might I suggest a more contemporary picture frame mantel with mosaic stone tile between that and your firebox? Love the near craftsman window shapes flanking the fire wall . . . use the height on both sides, / shallow shelves on one side can visually frame a swing arm for your television and give real storage on the other side.

Is that a window in center above the hearth? Is rock just a facade? Looks like you have a mixture of furniture styles. Windows look more of the modern style while drapes are traditional. I would say pick one style and go with that. From the windows I'd be leaning modern/ contemporary. If the rock is just stuck on wall take it off. Replace with horizontal wood planks stained same as your door casings. No mantle. If that is a window I would either have a stained glass insert made (again using modern lines) or do a faux stain glass painting treatment to add some visual interest.