This is an experimental idea. This was discussed on the Audiobus Forum.
Beta testers can create custom themes, and if I consider them that they fit with Mela I may include them in an update.
There's still some chance that I may provide users with the ability to create custom themes in Mela (in the App Store version), but I'm sceptical. Let's see how it goes in beta builds first.
Disclaimer:
Just to set expectations, I may not release any created themes by beta testers. This is an experiment.