There is an interface mod available for Pax Galaxia. The game and main menu backgrounds were made by Domenico, as well as the green buttons. I changed around the menu interface and some of the text strings. I have only tested it on Mac but it should work on Windows as well.
To install it, move all the files from the download into your Pax Galaxia folder on Windows, or if you are on Mac, right-click on Pax Galaxia.app, choose Show Package Contents from the drop-down menu, navigate to Contents/Resources/, and move all the files into the Resources folder. Note that you might want to make a backup of the original files.
You can download the mod here.
To learn about how to customize Pax yourself, visit the Guides page.