serperga: Do you mean the game beta or OSX? The red tint issue should be fixed with the current 10.14.4 beta 2.
Yor: Does that iMac have HDR support? A quick search online implies that it doesn't (EDIT: but it does; maybe the confusion was the bug mentioned below when applying the settings?). In any case, the darkness issue is a symptom of enabling HDR with an OSX system that doesn't support it, so if your iMac has HDR support, the game is not detecting that for some reason.
