I'll look into that.
BTW, a nice companion to this would be to have a 'nav' button that will make the window but not the buttons transparent so CFE stays active but you can see through it to the nav option. You can always hide it to control the nav program.
I've thought about that and there are really three solutions. The best is hardware based where you have light sensors to tell it what the ambient light is. Obviously not everyone will have such hardware available.
In the spirit of the FE being the main control program, I'd also suggest that CFE perform auto-dimming of the screen brightness. Right now, I use Shades to control dimming at night. All it does is put a non-active window at the front that varies in transparency. Maybe CFE could do the same either at sunset or on command.