Cool reader allows you to set text color, background color, background texture AND brightness settings for both day and night modes. You can also set a tap zone action to toggle between day and night settings.
I just tested this. I set day/night settings to be black text on white background, night mode at 5% brightness and day mode at 50% brightness. I also set long press on the bottom center of my screen to toggle between day/night modes. It worked.
Regardless, I prefer the light paper/dark paper background and prefer adjusting brightness by swiping the left edge of the screen.