I prefer accent walls to be those with no redeeming architectural features. If you want one wall to be a different color, I would choose the longest wall that has no windows, doors or a fireplace. If this isn't your furniture, then we can't suggest a color. Paint should work with the fabrics and textiles in a space. Bring those in, take fresh pix, and post as a new dilemma.

I would not paint. Right now it doesn't feel a part of the room and an accent color will only highlight that. I would focus on building around the fireplace and keep the eye low. Do something more like this:

Ditto. I can't imagine why they didn't center the niches on the peak of the ceiling; that would drive me a little insane (but admittedly I'm a little OCD that way)! Dry wall it over. Center the cable connections to the TV, then mount the TV on the wall. Find a low media credenza for under the TV, then add some floating display shelves on either side.

If you have the budget, it would be nice to have built-ins on either side of your fireplace. This can be done at a low cost with Ikea cabinets, you can look-up ideas online. Looking at the overall look of your house, I would look into changing your accessories instead of painting. Your wall colour looks quite nice online. However, although your accessories are coordinated, they lack in punch. I would get coordinated darker shades of blue pillows and buy feather inserts so that the pillows can stand-up rather than lie down on the sofas. You also need a larger artwork above the sofa. The area rug can also be in a darker shade of blue so that the sofas will stand out and it should be large enough for your furniture to sit on the carpet (at least the front) rather that have a rug that sits in front of the sofas. Your coffee table and mantel also need to be accessorized. Here are some ideas: For your dining room: I think white drapes on a black rod would look clip and nice with your wall colour. Again, I would put colour in the accessories. Since you don't have a pendant/chandelier, you can have a fairly large table centrepiece to give the room punch. I would suggest you reupholster your chair seats in a light colour (can be off-white or a blue/white/beige print that will coordinate with your living room. I would think this is can even be a DIY project. you can also consider to have some seat covers done which can be easily removed for washing. Your buffet also needs some dressing up. Here are a few ideas: