This summer Clean will become the default theme for Moodle but it will ship with an additional theme from Moodle HQ: More Theme. More is being designed to provide additional customization options for users who want to brand their site simply without being theme designers (all of the options will be customizable from the admin interface).
Not a lot of information has been released on the theme in the forums, but you can dig into “More Theme” in the tracker. The goal for the theme is “being able to set the basics (background colour, text colour, link colour, logo) through the UI”.
More information at https://tracker.moodle.org/browse/MDL-43786.
Sadly the theme doesn’t appear to be available at on the Demo or QA site yet.