Is black gloomy? No, it is not. Black is expressive and elegant. The requirement for use of black is a large area of the bathroom.
Choose glossy tiles for the bathroom walls in black. Shiny tile surface will reflect the light, not concealing space.
Lighting plays an important role in the bathroom with dark monochrome tones. If the advantage is given to black, the lighting should be bright. The presence of sunlight would be the ideal option. Hidden lights across the bottom of the walls would be a win-win option.
The mirror is an important detail for black and white bathroom design. Mirrored surfaces extend space.