IMO, accent walls are for helping out a room that has little architectural interest going for it. All that railing and fireplace are enough interest without a color change. A lot of us see gray as a fading trend, so the charcoal would be better for the entire space, but I love darker, rich colors.

I wouldn't want to bring more attention to that wall - there is enough going on...

You could use a few more pictures here I would do the fireplace wall the charcoal leave the fireplace I'm guessing whatever color it is don't paint it am I unless it's black if its black take a picture of it please cause we might need it to be is it to be white or another color

IMO first do the floors and then see what you want. I think the long wall is already way too busy so no accent wall there for sure as for the picture wall IMO accent walls are best done to enhance a space and I think that wall has a lot going on with the rsiling and the light already interfering with the art.