I am sorry I couldn't find an image example to share, but With a low ceiling compared to the room height, I would focus on window treatments, rather than a wall paint color. same color drapes as the wall color you choose (all the walls, not just the fireplace wall.)

Hang a rod at the ceiling height on ALL windows in the cozy Fireplace space. Layer the windows with a shade and drapery panels.

I would hang a stained or leaded glass window over the horizontal window above the mantel

Mount the TV on the wall.

I would have it drywalled over, I realize it might be a little complicated on the exterior, does it face the backyard?

Paint the entire space a neutral color, perhaps multiple shades lighter than the fireplace surround. Find some interesting white stone pottery for the mantel. Add an armful of chunky logs to the firebox, or birch logs to pull the eye down if you don't like the window. Done! The window gives you a view of the outdoors and works in symmetry with the side windows. The accent wall doesn't work because it chops up what is otherwise an attractive wall. Paint it like the rest of the room then leave it be.

And if you can't leave it be--so unimportant in the scheme of things, especially the budget--you could commission a stained glass insert.

Note to others with less than satisfactory fireplace walls, spend your budget on what's in the room itself--rugs, art, nice furniture, drapes--and not on spending your budget on some insignificant wall feature.

I would also recommend shades and drapery panels to make the wall appear less 'stubby' with the position of the windows.

I might even consider mounting the TV screen over the center window.