Gamma issues

[Bridge]

I finally got this up and running and I'm getting pretty good performance so far. There's only one problem - I cannot adjust the gamma at all. I can drop it all the way down to 0.1 and it is just as visible as it is at 1. It seems like this is a common problem although I haven't been able to find a solution yet. Does anybody know a fix?

P.S. I'm completely new to Linux (just installed the latest stable Debian yesterday) so please excuse my ignorance.