What is needed is alternating themes based on the real world day/night cycle. Even though when the sun goes down that arguable should be the time that screen time should be cut anyway.
If you are using X11, you can use xcalib to modify gamma/brightness/contrast of the color channels individually. My own quick hack is "xcalib -invert -alter" which simply inverts the colors. This probably breaks subpixel rendering, though, but IMO subpixel rendering looks like crap on low resolution displays and is pointless on high resolution displays.
