When is my screen supposed to be green?

The PGP public key: it is used to sign the currently running boot firmware.

I am confident one of them is your old PGP public key in a Librem Vault, and the other is either a PureOS or Qubes OS image on a USB drive.

It is generated as a binary file in /pureos/home/.gnupg/, or within a hidden directory along those lines if you are using PureOS on a USB drive. Otherwise it should be in /.gnupg/.

Here.