It changes the hue much like f.lux. If you're in a room with incessant ("orangish") bulbs, or any area without sunlight (which has more of a "blue" tone), turn it on. Let it be for a few minutes as it slowly changes the hue. Then, after a few minutes or so, go back and uncheck it. You should see a difference so long as you're in an area where it can match the ambient light correctly.