You might've not known this, but FBI has a theme feature. It loads them from /fbi/theme.

Here's how you can make your own themes:
  • Download the FBI repo from Github. ("Clone or download" -> "Download ZIP")
  • Make a seperate folder for your theme, and put the contents of the "romfs" folder in the ZIP inside the folder you've just created. You can dismiss the rest of the ZIP.
  • Edit the images. Make you you keep them in the PNG format and don't resize them.
  • The text colors are stored in the textcolor.cfg file, they're formatted as hexadecimal ARGB (Alpha, Red, Green, Blue). Alpha "FF" means full opacity, so you would probably want to keep that.
  • Done!
You can zip up your folder to share your theme, and install it by putting the contents in the "/fbi/theme" folder (create it if it doesn't exist), and your theme will be in effect the next time you boot up FBI.

Here's a theme I've done myself:

Download