I have an oak staircase that is black and white

If it were me I would go with white walls.

It's hard to tell color in the picture because it's pretty dark. Is that curved edge part on the bottom part of the top stair railing itself? Actually, it's pretty much your choice, but in my opinion, black and stark white, without other colors at all, are pretty much 'out of style'. Could you take another pic of the area from further back? That might help.

Any pastel or light color would go well with the stairwell. Gray, burnt orange, soft gold, many colors in vogue right now would look good with your stairs.

A pretty light sand color would accentuate the darkness and brighten up the area.

Black and white go with ANY color. Choose something YOU like.

I would paint it whatever color you like, and do be sure to tape off the stairs and put down a cloth drop cloth as you paint.

What about a soft blue gray?

This is my suggestion...... get some paint samples of colors you think you might like............ and paint some stripes in that area..... see which one you like best after looking at them for a couple of days..... then go with that color!!

Do some stencils in black on white part of risers of stairs

find a mural you like and do the rises by pasting it to them , you could even get something black and white or you could use a stencil

http://www.hometalk.com/diy/staircases/gave-my-steps-a-very-different-makeover-26110284

I would paint it any shade of gray since gray is a combination of B & W