[Loki]

I use the following:

export PS1='\e[0;31m[\h:\w]\n\$ \e[m'
in root's .profile and
export PS1='\e[0;36m[\h:\w]\n\$ \e[m'
for everybody else.

Then if I really need to do lots of rootly stuff I do:
sudo su -
and end up with a red warning that I have not left root (yeah, I know the prompt is # but a red prompt sticks out like dogs balls.

Whatever floats your boat, I guess.