Gamma adjustment doesn't work

[Urkle]

How about it you disabled the steam overlay?

Tested. Makes no difference. Assuming you had the 'Enable Steam Community In-game' option, that is.

What is the MD5 of the non-steam version of Amnesia that you have?

As the version released with the HIB has this MD5

2e2deb3907c515382631a1cd42dca60b 2012-05-23-1.2.1-HIB/Amnesia.bin

And the version up on steam has this

2e2deb3907c515382631a1cd42dca60b Amnesia.bin

My only guess is that something in the steam runtime is screwing it up (not the first time). You can try starting steam with the runtime disabled by doing this

STEAM_RUNTIME=0 steam