In-game Gamma Problem

[bluNEON]

Im aware this thread is a few months old but lve just bought the game on the mac app store as it was on discount for halloween and im having the same problems with the gamma settings, not sure why its doing this. I bring up the gamma but then it reverts to its original setting. I have the mid 2012 macbook pro and dont think its any graphic issues as the laptop is pretty much brand new.