The lighting toggle is the best idea I've seen in here so far. If it truly is an accessibility issue (which I can definitely see - no pun intended), that's a very common thing to have lighting/hue changes for. I'm thinking specifically of colorblind filters, which I see in most other games I play nowadays.
Game design wise, I also felt that not being able to see things properly myself was a fine reminder to turn on a light for my characters that also couldn't see in the dark. If I go at the game the way it is now I can definitely envision a situation in which I'll be slugging away at Underdark baddies with hella disadvantages and wondering why the game is going so poorly.
