I know this is trivial but there's a somewhat new monochrome GNOME icon that many third-party icon sets seem to miss - it's for a USB device that is larger than 8.0 Gib so it does not get a pendrive monochrome icon in Nautilus but not big enough to get a external HD one.
What is the name of this particular icon so we can tweak our icon themes to make Nautilus show the correct monochrome icon?
I'm attaching two Nautilus screenshots - one with the default gnome theme and another with gnome-colors. The device in particular is called "NIPPONIC" and I circled the 'out-of-place' icon.
Fundamental Axiom of the Universe (aka Murphy's Law): Whatever can go wrong, will go wrong.
First Digital Deduction: Nothing obeys Murphy's Law so well as computers.
Second Digital Deduction: Everything go wrong at least once.
Third Digital Deduction: Things go wrong even when there's absolutely no possibility of anything go wrong.