I think the first thing you need is better lighting. I'd ditch that open fixture that throws weird shadows and put in recessed lighting instead. And the paint color should tie in to both levels the staircase is connecting.

Agree with Sabrina about taking out the fixture that is throwing shadows. A few questions - What colors are the rooms at the top and bottom of the staircase? What is the gray area at the top of the stairs in the pic? Are you open to hanging a tall piece of art on the wood section?

It appears this is a closed stairwell at the top, so I wouldn't be too concerned with the wall color upstairs. The wood accent wall is the star of the show, so you just need a color that doesn't fight it or draw too much attention. I would also keep it fairly light. SW Shiitake is a favorite, though Malabar may work better with the gold and red undertones of the wood.

I might also considering replacing/stripping the handrail to be a wood tone to tie in with the great accent wall!