Is there a tutorial we can follow for creating a custom UI theme? If not, is that something we could get in the future, maybe in the 'Mini tuts!' section? I'd like to follow along with something more granular and explicit than what's in this lesson to gain a better understanding of that process.
While a GUI Secrets pack is in the cards, it's not yet in development. Though in the meantime you can check out this video by Nathan for an overview that's a bit more visually in depth than what I've gone over in the builder series.