http://stereopsis.com/flux/ i found this a while back and i really love it. i use the preset 'fluorescent' which only changes the screen to a warm mild tone. but basically the app knows your time zone and changes the screen hue slightly, which is easier on the eyes for long hours of use. also the normal hue of the screen has some of the same type of light as the sun, which keeps you awake, but this program takes that away so your computer wont keep you awake. good for me because sometimes i used to lay in bed on my laptop not being able to sleep for hours. just read the app page and give yourself a chance to get used to it.