Just a few questions, to figure out if it's a bug in the game's graphics or if it's a malfunctioning monitor:
When did it start?
Does the sky in Cape look gray?
Do other black things(Outside of FH, such as inside the browser or in an image) look gray? If so, Have you tried viewing the monitor from different angles?
Does black look grey in real-life?
To test the monitor, draw/view an image that's completely black. To test the game, make a material file that uses the image that's completely black. To test the computer, print the image that's completely black. To test eyes, try to find a real-life object that's completely black.