Do you have any trim in your house, that matches what you have now? You could paint it white, so it matches what trim, I see, however, if it matches other things, you are not changing, it would be best to leave it. I have seen way too many banisters in the last 6 months, that someone has painted, and they are a chipped awful mess. They look beautiful when people bought the houses, but, in just a short time, they look terrible.

Match the stair tread. You need darker than it is now with the very light walls.

How dark? Any ideas

Same color as stir treads.