Found this on the Microsoft Answers Windows 8 CP forum:

AnswerMicrosoft is releasing several updated display drivers via Windows Update for Windows 8 Consumer Preview. These updates may resolve a variety of known graphics issues. Please check Windows Update to make sure that you have downloaded and installed all of the latest updates, including optional updates.
To check for driver updates,
  1. At the Start screen, type Windows Update.
  2. Click or tap Settings on the right side of the screen, and then select Install optional updatesfrom the left results
  3. When the Windows Update control panel opens, click on “Check for Updates” on the top left corner to receive a fresh list of updates
Please note that after installing a driver update, Windows Update may continue to show the same driver update is
available until another scan for updates occurs. During this time, attempting to install this driver update again may fail with either an error code 0x80070103 or error code 0x800F020B. This is currently a known issue on Windows 8 Consumer Preview.
When this occurs, the driver should have been successfully installed on the first attempt and you can safely continue to use the PC. To avoid this issue, after installing any driver updates, click Check for updates to perform another scan and verify that no further updates are needed.
If you have all of the most recent updates and your graphics issue persists, please search for your specific issue in these Answers forums, or post your issue in your own thread.