A work around I've found is another "last chance" to update to Windows 10. Windows 10 - Assistive Tech Upgrade This is a lot like using a sledgehammer to hang a picture but its all I could find. Thanks anyway herf! Keep up the good work. DisplayLink, it's not for everyone...

@herf This solution worked perfectly! Thank you so very much!

Forgot to mention that the old laptop was attached to these same two monitors through the Dell docking station, and both monitors dimmed as expected with f.lux. Also, when connected to the dock, the laptop is generally closed, so the laptop monitor is turned off, and the Dell monitor (Monitor #1) is the main screen. Uninstalled and reinstalled f.lux, and expanded the color range again. Still doesn't work.

I noticed this came out yesterday. Looks like DisplayLink is working on supporting f.lux. Windows only. http://www.displaylink.org/forum/showthread.php?p=82958#post82958