I'm not saying it's a bad idea to tweak lighting/colours a bit (and it's certainly a good idea to increase "BG feel"), but BG1/2 weren't really as dun as people like to say. They were, I'd say, context-appropriate - at the start of BG2, you emerge from a dark dungeon into sunny, bright Waukeen's Promenade. Most outside locations during the day are light/vivid unless it's raining.