The ability to change the colors of the Volumio interface.
Using a preselected color -or- by using someones own image to for background. Even different button shapes.
Maybe I should have checked first, but a tutorial on how to “Skin” Volumio.
I think this is just a matter of playing with the CSS stylesheets for Volumio. They are found in /var/www/css (if you connect by SSH).
I think ‘panels.css’ is pretty important, but you’d just have to play with it to find out what everything does. Probably a good idea to back things up first though!
Search ‘Theme Selector Installation’ in Development talks, 
The difficulty was getting the knob to use css colours, but problem solved… 