Was looking through the api on https://neko250.github.io/pico8-api/ and I noticed the command gui_theme. It seemed to be something I enter in the splore console but does't work. Is there a correct way to use this? Has it been deprecated?

It looks like you use the Run application to open Pico-8 with these arguments. Example photo below:

It's not a console command. gui_theme is both a command line argument and a configuration option. Find the config.txt file for your operating system, then edit it in a text editor:

http://pico-8.wikia.com/wiki/Configuration

Locate "gui_theme" and change the 0 to 1.

You can also specify -gui_theme 1 on the command line. For example, in macOS, run this in Terminal, changing the path based on where you put the PICO-8 app:

~/PICO-8/PICO-8.app/Contents/MacOS/pico8 -gui_theme 1

Linux is similar, for wherever you put the pico8 binary. You can also do this from the Windows command prompt, though here's another way (similar to what Remagamer is describing):

https://superuser.com/questions/747684/how-can-i-run-an-application-with-arguments-from-windows-explorer

http://pico-8.wikia.com/wiki/RunningPico8

It's undocumented, but if you set the value to 2 (or above? I forget) you get a black background.

Thank you all :)

"It's undocumented, but if you set the value to 2 (or above? I forget) you get a black background."

WAT. 😲🤯