Currently when using vibrant visuals and applying the fog effect, while the fog itself will actually push and pop when applied, the color does not come with it, leaving Minecraft:hell fog color looking grey and dull
To reproduce this, simply have vibrant visuals enabled, enter a world and apply any / fog to your character, I recommend using hell or warped forest because it comes with a large color difference, but the expected result should be the fog rolling in with the color applied, though the actual result is just the fog rolling in as a standard grey opaque fog color.