When should the valid visual cue be shown to the user on a pre-filled form field?

It makes sense to show a valid visual cue (eg: green border, green check, etc) when a user is filling a form field and the data is considered valid.

What if the user opened the form with pre-filled data? For example, when editing something.

When would be the appropriate moment to show the valid visual cue on form fields that were not edited by the user?

When the form is loaded?

On focus and blur events?

When the form is submitted?

Never?