To run this on Debian 10 (Based) systems:

1. Install openrazer
sudo apt-get install openrazer-daemon openrazer-driver-dkms openrazer-meta

2. Make openrazer-daemon auto launch at login
I did this using a systemd service, the service file is added to this repo.
Make systemd able to find the file by symlinking it to the right directory, to run the following command, make sure you're in the directory containing the service file.
sudo ln -s "$(pwd)"/openrazer-daemon.service /usr/lib/systemd/user/openrazer-daemon.service

Now you can enable the service for the current user:
systemctl --user enable openrazer-daemon.service

Reload systemd:
sudo systemctl daemon-reload

And finally, start the service:
systemctl --user start openrazer-daemon.service

The openrazer daemon should now be running, and start again everytime after login.

3. Now make sure theme_daemon.py gets started in the background after your displaymanager is started. For me, this is done in the .xsessionrc file in my home directory. For other displaymanagers this file could be called .xprofile or something else.

I put the following line in my .xsessionrc:
/home/USERNAME/bin/razer_blackwidow_theme/theme_daemon.py &
Make sure you use the right name for your home directory, and change the path if you put the python script in another directory.

4. Now reboot/restart your displaymanager, and check if the keyboard theme works (I do this by checking the numlock and capslock keys)