If a player stands near a colored light source that contains a modified lightvalue (over the expected value 0 to 15) then render fog will be altered significantly. In most instances, the renderfog is darkened significantly as if the player was in a cave.

The next steps will involve taking a close look at the brightness variable as it makes its way from world->entityPlayer->renderfog

I'm not certain if there are any more pieces to the puzzle or not.

I think this is fixed.
Confirm?