$ PS1='\[\e[1;31m\][\u@\h \W]\$\[\e[0m\] '
It is useful to set a different color for the shell prompt in different deployment environments like dev/test/production, so that you don't mix up your multiple windows and do something by accident in the wrong window.
To make the color stand out even more for root users, the inverse color can be interesting too:
Other color examples:
You can learn more in
Your terminal program must support colors, of course ;-)