The values from the configuration file are not applied to the fog when loading the mod. Values are only applied when changing values via the in-game configuration editor and only until the game restarts.

fog-looks-good-now.json5:

{
	"biomeFogs": [],
	"defaultFogStart": 0.0,
	"defaultFogDensity": 0.0,
	"useCaveFog": true,
	"caveFogDensity": 0.8,
	"caveFogColor": 3355443
}

latest.log