Paint the walls in the room a very pale pinkish-white color with an eggshell finish. This will coordinate with the shower and floor and soften natural light in the room without making the room feel overly feminine.
Paint the wall behind the sink and toilet a slate gray. This provides a dramatic focal point in the room and brings the floor color up into the space.
Paint a wood vanity cabinet a slightly darker color than the wall. This will coordinate the room and add definition to the lighter pink walls in the room. Add drawer pulls in matching metallic finishes.
Frame a wall mirror over the sink with a metallic frame that will match the existing metal finishes in the room. For example, if the shower and sink fixtures have a brushed silver finish, frame the mirror with a brushed silver frame.
Install a light fixture over the mirrors that feature a matching metallic finish. Keep the fixture simple so you don't take away the focus from the mirror frame.
Paint a medium sized wood box with black paint. Once dry, paint with a pink paint and distress with sand paper to see the black beneath. Place next to the marble shower and pile a collection of plush black and light pink towels.
Frame and hang a large art print that has both black and pink colors in it to tie the space together. A hand-colored photograph or floral print will fit the bill.
Hang black wood shelving to provide additional storage and display space. Use frosted white glass containers to hold toiletries and to soften the look of the black features in the room.