Nocturne is a Mac OS X program which can change your display colors in various ways to give you a color scheme more suited to low light conditions (such as at night).
The makers of our beloved Quicksilver released another interesting utility called Nocturne, which inverts your Mac's screen colors (turns white to black). Mac guy Merlin Mann explains:
For years, you've been able to do something similar by hitting "Ctrl+Opt+Cmd-8," which invokes "Switch to black-on-white" in Universal Access options (go ahead and try it, then hit it again to return to normal). While A1c0r's improvements on this may seem subtle, they're very useful for allowing you to tweak your own preferences and minimizing distracting, full-color solarization effects.