Why would all theme background colors disappear after moving to different server? A site using MAYO 7.x-1.2 was moved from a Windows IIS to a Linux server. Shortly thereafter, all background colors defined in MAYO settings (and also any custom CSS) have disappeared. Also gone is the custom background color for dropdown Nice menus – it just goes transparent. Other than the bg color, main content and layout are OK. Perhaps there is no relationship of this to the server change, but in any case I haven't been able to debug this with anything I tried. The PHP version is now 7.2, maybe that is related, and I'm not sure what it was under the Windows server. Site needs to stay in D7 for now, although a D8 upgrade is planned.

Also note, I was aware that this is an old version of MAYO that should have been updated long ago. I hesitated to update because I had modified the template file to get an additional region, and wasn't sure how to apply the update while preserving the custom region. (Could use some advice there.) In reading the docs about the security update, it seems the circumstances for risk don't really apply for this site.

Advice on either of these issues will be much appreciated.
First , Check Administrator -> Configuration -> Media -> File System to personalize your tmp path. Make sure to use relative paths and have the right privileges for your webserver.

After than Check permission of the /sites/default/files and make sure it's writeable by your web server.