While working on Rave Cage Carnage at Tonkotsu Games, I was responsible for Game Design, as well as UI Design.
The core focus of this design was clarity, bold shapes (square backgrounds and panels), as well as identification by colours.
The darkest colours should always be the background, commonly in a very dark grey-tone. Selected elements (most commonly buttons) and dynamic panels are outlined with a white outline.
On top of that, white is generally the colours of interactive elements. Additionally, some surfaces have colours on them, such as buttons which are representative of outfit colours (visible in the Shop UI) or buttons based on enemy types (here in blue due to the enemy type in the Library UI).
I also worked on a mobile version of this UI.