Hello Blizzard. I cannot change the gamma and the fog or war is litterary pitch black.
Make sure your display is showing black colours correctly. Use the following site to check black levels.
http://www.lagom.nl/lcd-test/black.php
All 15 of the low black blocks should be visually distinct from the pure black background. If not then your display is incorrectly configured.
If the display is HDMI this could be caused by range mismatch. HDMI is a TV orientated standard so does not use the full 256 value range for each colour component. One either needs to set the display into PC range mode which does use the full 256 value range, or to tell the GPU driver to output in reduced range mode. The lower black colours will be cut off if the display is in reduced range mode but the GPU is outputting full range mode.
There is no reason for gamma to exist in modern games as its purpose, to correct for CRT displays having different gamma responses, no longer exists. All modern displays use an sRGB based response. It never was used correctly by Warcraft III anyway as it was meant to correct for lighting and blending mathematics being linear but instead defaulted to no correction. The way it was implemented did conflict with any applied colour calibration as it uses what used to be known as the DAC LUTs which are also used to implement colour calibration.
If you want a brightness or contrast setting, then that should be applied to the HDR shader as inputs. This has little to do with Gamma and instead would be range remapping.