I always add something like this to my /root/.bashrc
Code:
#Make prompt red when logged in as root
PS1="\e[1;31m[\u@\h:\w]#\e[m "
...which also adds user name and path to the prompt...
Also, if you do not have a /root/.bash_profile, you will need to create it and add these lines:
Code:
# Get the aliases and functions
if [ -f ~/.bashrc ]; then
. ~/.bashrc
fi
See man bash, INVOCATION for the precedence order of config files and how they are loaded.