This started happening for me yesterday. Not sure what caused it. Went to the RAD zone the day prior. Had no issues. Played for about 9 hours yesterday and had no issue. But when I logged back in for a quick hour of play last night, everything was suddenly darker. Tried using NV to get rid of it but that didn't work. I'll check again when I get home from work. Maybe it decided to fix itself.
Specs:
NVidia GTX-970
Intel i7-5930 3.5
32g ram