Paint the fireplace section of wall the dark blue so the stainless frame stands out. Done. An interest stainless metal art sculpture over fireplace would be nice. I will post some ideas.

Paint the cable/plug covers when you paint.

Something like this only hang it upright so it covers the plugs. Hope you aren't mounting a TV!?

This "mixed metal" would be great. If you do mount the TV above fireplace (ugh-we designers hate that) then something like one of these on each side wall would be interesting. Keep it modern in any case. If you are doing dark blue, make sure you get a primer that works with your color. Saturated colors don't come out well, unless you properly prepare your walls. But I love the dark blue with your other wall colors and the metals.