Hi,
We can confirm that a cache issue was keeping us from seeing our changes being saved in the backend.
However, even then, we did not see the results of our settings reflected in the frontend.
As we realized that the site has gone through some changes over the years, we've created a new, clean develop site from scratch and copied the SP PageBuilder content to this site. Also I created a dummy page using a Joomla core article and the HelixUltimate templage, so we can view the template without SPPB content. See hidden content for the url of this page and of the new develop site.
On this new site we still have the same issue. On the dummy page you can see that the body background is white, though in the settings we selected a dark color (#141328).
I created an account with the same details as I did for the live site. I repeated those in the hidden content, in case you want to check.
Kind regards, Frits