Nextcloud 12 theming, login screen solid background color

For background information, please see these posts:

  1. https://github.com/nextcloud/server/issues/1414

  2. https://github.com/nextcloud/server/pull/4617

  3. https://docs.nextcloud.com/server/12/developer_manual/core/theming.html

So, I want a Nextcloud login screen with a solid background color instead of the default image.

With Nextcloud 11, I achieved this as described in my post to the link #1 above.

With Nextcloud 12, it is supposed to be possible to set a solid background color as described in #2 above, however I haven’t found this documented anywhere else and, as I said in #2, this is not working for me. Also with Nextcloud 12, my solution as used in Nextcloud 11 is no longer working.

What does work for me is to follow the more flexible theming procedure described in #3 above. This does allow me to set a solid background color for the login screen, or a color gradient, plus allows me to specify different colors for background and Login button. The result can be seen here: http://mcloud.mcmaster.ca/.

However, I have one problem that has come up with using the #3 theming method. I’m am seeing these error messages logged continuously, and I haven’t been able to determine yet what the problem is:

{“reqId”:“WZwpXTFBqKnAzr-NwtZ7BgAAAEI”,“level”:2,“time”:“2017-08-22T08:53:49-04:00”,“remoteAddr”:“1.2.3.4”,“user”:“x”,“app”:“l10n”,“method”:“PROPFIND”,“url”:"/remote.php/webdav/x",“message”:“Failed to load /www/sites/mcloud.mcmaster.ca/html/nextcloud/themes/Mcloud - json error code: 4”,“userAgent”:“Mozilla/5.0 (Macintosh) mirall/2.2.4 (build 1) (Nextcloud)”,“version”:“12.0.2.0”}

The directory mentioned in that error message definitely does exists, and that is how I achieved the theming that can be seen at the url I gave above. Perhaps something essential is missing from my theme directory, but it’s not clear to me what may be missing and the error message above is not very helpful.