Control button state on edit form if nothing has changed?

On the New Record form, I can use field validation rules and display rules to prevent user from clicking submit button until key fields have got data in them. I’m especially interested in the display rule. With a new record form, I can set the background color of the Submit button to light gray and disable the button until the user has put something into required fields X, Y and Z. And once those fields have data in them, the button’s background color changes to green and it becomes clickable. Great — exactly what I want.

Problem is: I can’t seem to do this the way I want with an edit record form. What I’d like is for submit button to default to gray when the edit form is opened, and turn green (and become clickable) ONLY when a change had been made to the form. Is there a way to do this?