I'm running a Icewind Dale: Rime of the Frostmaiden campaign and as I'm sure those who've read or played this campaign knows, it's always dark. This means that I always have Dynamic Lighting on. The problem is that sometimes, like in blizzards, it's the snow that is hindering the player's line of sight. The ability to change the colour of the blacked out area would go a long way to set the mood and distinguish storms from nights. Beyond my hyper specific situation it would be useful for more subtle storytelling. Players drudging through a desert encounter is going to feel warmer if the usually cold black is replaced with a warmer black. Or have it be a slight slime green in sewers so sticky and slimy, even the darkness feels sick. My point is that having other colours than black would help us project whatever mood or theme we as DMs want to encourage in our players. Besides, if we can already apply filters to darkvision , why not be able to do the same to the Fog of War ?