Strange graphics glitches/grainy/256 colours looking/pixelated with white spots/low quality/etc in Penumbra: Overture.

Usually You can access the settings for your graphics card by using the tray tool icon, or you can right-click on the desktop and select properties, the settings tab, click advanced and then select the tab for your graphics card.

Graphics that looks to be in 256 colours/over-saturated/grainy, if you have an ATI graphics card.
This probably is because the A.I optimisation option is enabled in Catalyst Center. Try turning it off. We do not have access to an ATI video card so we can not make a guide for this.

Graphics that looks to be in 256 colours/over-saturated/grainy, regardless of what card you have.
In the control panel for your graphics card, make sure that Texture preference is set to High Quality for OpenGL if you have an ATI card. If you are using a NVIDIA card, make sure Image settings is set to Quality or above in the Performance & Quality settings menu.

You can also try turning Post effects off in Penumbra: Overture under the Options -> Graphics -> Advanced.