Signify that some input controls map to private information

I'm developing an app meant to be used by a school; user personas are teachers and students.

Teachers can add exercises to the app database through an editor. Some of the fields of an exercise are meant to be public (i.e. shown to students when they see the exercise), and some are hidden (only visible to teachers for internal management purposes).

This is what the editor looks like:

For example, the field "exercise label" and "solution" would be hidden to students, whereas the "text" field contains public data.

I'd like to somehow visually differentiate the inputs to signal which contain public information and which contain information that's only visible to teachers.

I'm thinking maybe a differeng background color or border, but I'm using so few colors in the UI as of now that I'm afraid it'd look inconsistent or out of place.

How would you go about this?