I've been using an aperture science theme I made for MacOS's built in terminal for years. I was able to import the color scheme, but I there seems to be no way of using a custom background. It's not a deal breaker for me, but it would definitely be a nice to have feature and one I can only assume would not require an incredible about of time to implement.
I’m asking for custom background images, which exist in the macos terminal, but seem uable to be imported via an exported theme or added otherwise at present.