Limited Color Mode
This is no biggie, but I just thought I'd mention it now that I've figured out when it occurs.
The "f.lux is in limited color mode" popup on the taskbar occurs after a Windows 10 upgrade (i.e. one Windows build to the next). I see this a lot on Insider because I'm updating builds at least a couple times a month, but I bet it also happens twice a year for people when they upgrade Windows (like from 1703 to 1709).
It appears for the first two, possibly three, boots after the upgrade.
Yes, it is true - we prompt 3 times per windows version, mainly because Windows has been resetting the adjustment on major upgrades. And if you never click the notifier it will do it on every Windows upgrade.