Have you ever wondered how the device lock icon colors come in the device applet of Qubes OS? I saw those everyday, but, never bothered to think much. The guess was the VM where the devices are attached (because those names are there in the list). Yesterday, I was asked for a proper answer by Nina, I decided to confirm the idea I had in my mind.
The way I am learning about internals of Qubes OS, is by reading the source code of the tools/services (I do ask questions to developers on IRC too). As most of the tools are wriiten in Python, it is super easy to read and follow. The code base is also very to read+understand.
In this case, the USB devices get the color from the label of
sys-usb VM. This
is the special VM to which all of the USB devices get attached by default and
label is the color attached to the VM (window decoration and other places). The
PCI devices get the color of
black by default.
Just for fun, I changed the color to
Purple, a few more colors in life always help :)