I bumped into what looks like a very useful resource:
However, it is not easy to find, and I cannot find any “command reference” directly linked from the documentation page. A more navigable page (similar to the help tab in the Qt Viewer) would be very useful for many, I think. It would be great to google “geant4 /vis/geometry/set/colour” and land in
https://geant4-userdoc.web.cern.ch/UsersGuides/ForApplicationDeveloper/html/Visualization/AllResources/Control/UIcommands/vis_geometry_set.html.
Or is there anything like that already available and I am just missing it?