Built in book shelves in white would look great!

Great fireplace! Some big black & white photos with white mats in black frames would kick the drama up and give you some more reflected light.

I agree with Terracegallery. The white to match what you already have, of course. Are those roller blinds on the windows? I think floor-length white sheers would look lovely there and give a sense of lightness. And I'm not sure the heavy black lamp is doing you any favours in the afternoon. A lamp, yes, but with a substantial base in a pale colour -- which might then sit on book shelves built to the height of the fireplace mantel. I think on the sofa a throw pillow a lighter version of the wall colour, and another that echoes the ceiling, both preferably in a fabric with sheen, would be good. You have a room whose beauty is in its austerity. Don't mess with it too much.