It seems to me that the vast majority of the users of the application are going to be as a result of hosting services (people like me who use Site Ground, and others).
As a result we don't have the ability to define the theme which we use on our webmail, but there are certainly some excellent themes being developed for the application.
It would be great if there were a configuration option to specify the theme which you were using. This would give the development team the opportunity to pick the cream of the themes which are developed to be included in the release of the product.