Just upgraded from Civil 3D 2010 32-bit to Civil 3D 2011 64-bit. Over the years several user-defined color books were constructed using the Autocad Color Book Editor. With previous upgrades, these ACB files were simply transferred to the new version and worked OK. However, having upgraded to 2011, when the color books are opened, instead of the original colors, the color pages are corrupted, showing what look like Pantone red, green, and blue colors.
I have been in contact with Autodesk, and they have told me that this is a known issue that will be addressed in Civil 3D 2011 Update 01. In the meantime, they said that they might be back to me within 24 hours to see if a Hotfix or other files can be made available, to fix the problem.