Diablo 2 Mac brightness problems

I just started playing Diablo 2 LoD on El Capitan. The game is very dark, and when I adjust the gamma in game settings the brightness does go up, but a couple seconds later immediately drops back down to baseline. Doesn’t seem to matter if I’m playing windowed or not, or what resolution I’m using. Any ideas?

it does suggest that the game resets the settings. brightness however can be changed in the system. it should be somewhere in finder but, my mac knowledge is very outdated. blizzard will no longer help however.

This is independent of my computer’s brightness. The contrast and gamma settings in-game always revert back to some default setting that is very difficult to see after a few seconds.

what kind of gpu do you have? most gpus have a control panel for brightness. that is worth checking.