The Nocturnal filter desaturates your photos and adds a touch of blue and teal. Add the Nocturnal filter by clicking the Nocturnal icon on the Filters tab of the toolbar.
Use the Brightness: slider to control the brightness of the image. Darkening the image will increase the amount of purple. Brightening the image will increase the amount of yellow.
Use the Strength: slider to adjust the strength of the filter.