This color usually means that such files are not part of the project itself.
In this case, this means that the folder is excluded and then re-added back to the project as an External library (via PHP | Inlude paths ) - this way you do not see ToDos from them in your ToDo list; your own code refactoring does not affect / does not interfere with libraries and other similar things.
You can edit colors in Settings/Preferences | Appearance & Behavior | File Colors Settings/Preferences | Appearance & Behavior | File Colors Settings/Preferences | Appearance & Behavior | File Colors .
This color refers to the Non-Design Files area.
Here are a few options.
Change the color of this area record (by double-clicking on it) to any other that suits your color scheme better.
Disable the selection of files in the project view using background colors by unchecking the Use in Project View check box.
Use another GUI theme that already provides more appropriate / correct colors.
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