Let's gather some informations:
1. What graphics card(s) do you have?
2. Do you have installed proprietary graphics drivers (from nVidia, AMD, Intel etc.) or open-source provided by Linux community?
3. What is displayed in console during AC start, in positions: "Renderer:" and "Driver:"?
4. Does gamma changing work in other games (for example in Sauerbraten and Tesseract)?
5. If you have Windows on your computer with Linux, in which gamma changing doesn't work, that does gamma changing work in Windows?
1. What graphics card(s) do you have?
2. Do you have installed proprietary graphics drivers (from nVidia, AMD, Intel etc.) or open-source provided by Linux community?
3. What is displayed in console during AC start, in positions: "Renderer:" and "Driver:"?
4. Does gamma changing work in other games (for example in Sauerbraten and Tesseract)?
5. If you have Windows on your computer with Linux, in which gamma changing doesn't work, that does gamma changing work in Windows?