Trying to change it on preference menu, it's a buggy and wont save change. So this a tip to change it.
- Open menu Edit > preferences
- On left vertical tab, choose Editor
- On top tab, choose Editor Scheme Designer
- Write down New Theme Name with your own custom name, and click Save Scheme! button. You need to remember this name, just in case not showing up for next configuration.
- Click Save
If your custom name doesn't show up, you need to repeat those steps from beginning. And if your custom name exist, just on Theme tab. Choose it and next step you can edit color.
Hope this help.