Hi Shazbot, you can change the viewport background color as Marco shows above. There is not currently any bundled up way to switch background colors for UI elements like buttons. It is possible to change the UI, but doing so currently involves editing the HTML that defines the UI inside of the \ui folder, it's not that easy to do right now unless you're familiar with editing HTML already.

In the future I want to add some options for defining UI themes and switching between a few prepackaged ones, but right now working on new modeling tools has taken priority over that.

- Michael