From reading the documentation, "theme-color" appears to be used to
style the browser's chrome, which is done by some Android browsers and
also Vivaldi. This is most useful when the site actually _has_ a
colour. If you look at the homepage of Bibliogram, it has a
distinctive red theme. If you look at CloudTube, everything is greys.
I'd prefer if the user or user-agents gets to decide their favourite
colour, rather than us forcing a rather boring grey on them, so I'll
reject this patch. Thanks anyway though, I really do appreciate the
efforts!
As always, let me know if you disagree with my assessment.