Is there a setting somewhere to select the theme file?
Do I need to rename dark to default?
Basically, what are the mechanics of changing the theme?
Have you tried it with the Arduino IDE not running?
Make sure the file is not open in any other program such as this XML editor you mentioned.
Question - what is the term for the message box?
most of that file is a mystery.
I've done my best to document the theme properties here:If you find the purpose of any of the properties I've documented as "Doesn't appear to have any effect." please let me know and I'll update the documentation.