When you set the ambient light of a given dimension to a value below zero, like -0.1, the Night Vision effect no longer lights up darkened areas.

The motivation here was to make a datapack that darkened the caves and shadows of the Overworld, but this bug has been a big problem in dev.

With some experimenting, it looks like the cut-off point for the Night Vision effect breaking happens when the light level of a block is at 0 in a dimension where ambient light is set to -0.018. Anything above becomes hyper saturated, anything below becomes pitch black (see attached).

I think the problems has to be with the way the night effect "lights up" darkened areas. On a side note; Optifine torches work fine in dimensions with negative ambient light, regardless of the setting. Maybe that could be helpful?

Also, confirmed for 1.16.3. I've attached a few images of what it looks like in an Overworld with an ambient light of -0.02, along with a one-file datapack to show what I mean. The only value modified is "ambient_light" in overworld.json.