The comments have their own color, so it must be possible to create a custom theme that would use the same color for comments and the background. You can select the theme via the IDE's preferences and it takes effect immediately after you exit the preferences dialog.
I don't know the process of making a custom theme for Arduino IDE 2.x. I remember someone providing some information about it in the Arduino IDE 2.x repository's issue tracker, but I didn't find it after a quick search. The important thing to know if you are researching the subject is that the Arduino IDE 2.x is built on the Eclipse Theia framework.