My personal opinion is with a black lounge, it's good to have some stronger colours. I have black framed windows, so I chose to paint that wall teal, the rest white, timber desk and earthy coloured floor tiles and use red as an accent (for lamps office accessories etc). So teal, red, timber, black and white is my office colour scheme.

Love that door. I’d use floating full length. Or just full length with brackets. If you google Katrina Chambers, she has full length in her study for inspiration.

Are the white bits blinds ? Do they open to the outside world ? Venetians , wooden venetians , curtains , anything would give those a lift ! Probably each one around 60cm wider than the window , with a natural timber valance ( mounted inside the window frame , as opposed to being part of it ) . Lauren Shiels sugggests dark Navy walls , I'd go more a plum burgundy for the walls , although that would depend on your taste , and the other rooms . Striped cushions in the same plum and gold -- warm colours . A tall leafy plant if you keep the couch where it is , or maybe even if you move it or change it .

HU-624382943's comment about speaker placement is important. As far as quality listening goes (whether you like listening to music seriously or want to enjoy fantastic sound when watching movies, you want the speakers on the narrow wall (pointing towards the set of paned windows), not on a long wall. The challenge, of course, will be to get them sufficiently spaced, since you have the bookcase on the right and the cupboard (with or without doors) on the left, as well as the door to the room itself. (That door looks uncomfortably close to the cupboard doors, incidentally.) Unless you choose to suspend your directional speakers from the ceiling – which could be an option – you'll probably be limited to the width of that central section of wall, i.e. immediately to each side of the TV.