Found the answer - it's a tiny icon, a few icons to the left of the clock and battery-life icon.



  • Found it! Had missed the following sentence about finding the Preferences to the left of the clock. Amend "You can open up Preferences any time to view and change your f.lux settings" to "You can open up Preferences any time to view and change your f.lux settings. The f.lux icon is to the left of the system clock, in a bar at the top where you might also see battery life, the WiFi and Bluetooth icons, and other items".