After installing RHEL/CentOS 5, I noticed on both system, vim under root user has no color even though I have the correct .vimrc in place. Finally found an answer in Red Hat KB. It seems that in version 5, root user by default uses a minimal version of vim that does not support syntax color. [...]

Described below are several methods for shooting yourself in the foot using various programming techniques.
How to shoot yourself in the foot