A powder room is the one place you can go all in, and Soft Black is the move. This deep, almost-charcoal black wraps the walls and turns a tiny half bath into a jewel box. With no natural light to fight, the darkness feels intentional and rich rather than gloomy, and it makes everything you put against it, especially metal and porcelain, look more expensive.
To keep that black from swallowing the room, edge it with Bright White on the trim, the ceiling, and around the mirror so the lines stay sharp and clean. Then warm the whole thing up with Brushed Brass on the faucet, the light fixture, and the hardware. So black on the walls, white on the trim and ceiling, and brass on every metal touch point, that is all it takes for a small room with a big personality.