PS1 command line prompt AFTER su

[s2scott]

As established in the /etc/profile, I have the following 'PS1' custom prompt:

PSGreen() {
print "\[\033[00;32m\]"
}
PSRestore() {
print "\[\033[01;00m\]"
}
export PS1='$(PSGreen)\u@\h/\w\$(PSRestore) \$ '

It works great for user login and root login; however, it does NOT appear to run (or to be of any affect) if at the command line post 'su'

Does anyone know which 'profile' or '.profile' is invoked when 'su' is run and where I should place this script fragment? (I have tried /root/.profile and several others.)

With thanks,
/S