A default preferences file can be imported is available to make the code readable on a dark background: .
Before importing the script editor preferences it is a good idea to first backup your preferences to be able to restore them later.
In order to backup, go to File -> Export, and from General select Preferences. In the next screen select which preferences to export, choose a file name and location and click Finish.
To import the script editor syntax coloring preferences:
To restore the syntax editor coloring: