The background of Arduino IDE has changed to blue.

[SF433]

The screen suddenly turned blue during the test for downloading from Board Manager after entering .json into an additional Board Manager. Is it possible to solve it?

[per1234]

Hi @SF433. You can fix it by following these instructions:

1. Select File > Preferences from the Arduino IDE menus.
   The "Preferences" dialog will open.
2. Uncheck the box next to "Use External Editor" in the "Preferences" dialog.
3. Click the "OK" button in the "Preferences" dialog.

You will now find Arduino IDE is restored to the editable state.

If you have any other problems or questions, please post on the Arduino Forum:

https://forum.arduino.cc/

I'm sure we'll be able to help you out over there.