I just started using f.lux because I've been having insomnia issues and it seems to be helping immensely. I'd like to take it one step further and find something that can change my windows 7 theme colors to dark when the sun goes down. So during the day I can have my bright light-blue taskbar, window frames, etc... and when nighttime rolls around everything will switch to dark mode. Something like what happens on a Garmin GPS when the sun goes down, basically the colors reverse and it goes into night mode.
OS X and Firefox suggestions are extremely welcome as well, since I use both a lot.