To make the prompt red when you’re running as root add this to /root/.bashrc:
PS1=”\[\e[31m\]\h:\w#\[\e[m\] ”
To make the prompt green when running as a normal user add this to ~/.bashrc:
PS1=”\[\e[32m\]\u@\h:\w\$\[\e[m\] ”
See the shell man page and search the web for ANSI Escape codes for more info on the meaning of the escape sequences.