author of f.lux here.
DisplayLink does pass through DDC/CI commands to displays. We've had an implementation to do this for a few years, but we've been cautious to support this for a few reasons:
Most displays store color settings using an EEPROM, and these typically have a finite number of write cycles. We could get away with changing things a couple times a day, but gradual fading like we do would wear out this hardware quite quickly.
We've observed some variation in how displays implement gain controls, so the colors don't always look like we expect. Similarly, some displays flash, etc.
DisplayPort-connected monitors (read again, it sounds like DisplayLink) are often omitting these color controls entirely.
The communication channels available do not usually tell us if things worked or not, so it's somewhat a crapshoot overall.
All this said, we will probably add some simple controls to push color commands to DDC/CI in a future version, but it might not be so automatic.