love the wall color! A rich cocoa makes the small entryway seem grand. Black semigloss paint on the railing and accents of crisp white create a bold contrast, one of the keys to livening up a neutral palette.
When making a collage going up a staircase keep in mind to mimic the staircase lines in your collage. Also make sure to measure on every second or third step the distance from the collage to the stair to make sure it has the same distance consistently.