Tall greenery or sculptural reeds/bamboo, etc. in tall pots, is one idea.

Large piece of art that pulls your colors together.

Why not add another accent color on the window wall - but stop it between the two windows. Wall paint does not have to cover the full width of a wall - there are NO rules. Maybe red is on that wall then stops and turns back to that great gray you have where the mirror is -

I think that wall is perfect for artwork ( as suggested ) . I would pick up on the red accent color that you have and get some art that has red in it. See picture below :)

I would lean an oversized mirror against the wall

I agree -- art is the perfect solution for that wall. It would tie the room together. An abstract or minimalist piece would be especially nice.

Christi, on behalf of Thos. Baker

Agree again! Drapes or beige sheers would be nice.

Christi, on behalf of Thos. Baker

I love the look of the art on the wall as it doesn't take up much room and doesn't create clutter but pulls it all together. The drapes look great as well but it seems pretty tight in that area. Keeping it simple, yet elegant is key.