How to indicate a checkbox/toggle is "always on"

I have a group of toggles (styled checkboxes) in my interface to activate/deactivate the visibility of input fields in a form in he front-end. Two of those inputs are required for the form to work so they are always on. I would still like to display the toggles to show these fields as "on".

How do I clearly indicate these fields as "on" but disabled for the user. I've tried: grey (looks if they're off) and darker green (doesn't really communicate the functionality).