This is in very early development for a project I'm working on, it's also important to note that the sudden shift to black towards the end is a bug that's only apparent in the Cycle Test for video purposes, the video is sped up by x16.
The system is based off the Server's time (Europe/London TimeZone), and supports different fog depths depending on the season of the year and the brightness (Brightness was disabled for the Cycle test), whilst it won't offer anything for in-game, it's to add an extra layer of emersion for seasonal events, (Halloween, Christmas, Easter etc etc) where we plan on having different events in the day and night.
This is still work in progress, and it might even get scratched down the line. It also supports reversing from night (black) to dawn, but for whatever reason, the Cycle Test was having issues with it.
I know it's nothing amazing, but most of the systems I've seen posted here across the years don't use interpolation for fog changing colour, and just suddenly flick to the next colour, similar to Black Fog bug in the cycle test at the end when switching to night.