I found it:
cat /etc/skel/.bashrc
This is the default .bashrc for new users, which contains the code block along with some other colouring and stuff. The root users however gets a minimal variant from /usr/share/base-files/dot.bashrc.
Means if you login with another user, like dietpi, the adjusted terminal header should be there already, and the adjustment is hence only needed for root. And an alternative would be (if /root/.bashrc is still the original one):
cp /etc/skel/.bashrc /root/.bashrc