I didn't invent this totally; i picked it from some default Debian 
.bashrc years ago. I bet you can still find at least part of it in the 
default .bashrc, although commented out. All these \[ escape sequences 
are recognized by the terminal / terminal emulator to set the color. I 
think they come from the vt100 or a descendent.
The prompt above writes
the chroot name - if any - in the default color, between parentheses,
then "root@hostname:" in red for root  (green for me and  magenta for 
www-data),
then current directory, in blue,
then "# " in the default color

     Didier