How do I change the theme? I'm using the Dashboard module that comes with Drupal core. For roles that are not administrator, it is empty (permissions are set). I'm pretty sure it is because the theme isn't viewable. (Other roles do not see the backend theme.)

How can I change the dashboard theme to a custom theme?
For users who have access to Dashboard, remove their access to "use admin theme"; then they will by default use your theme.