How to make sure that the change has been implemented in the Form?

Hi

If we amended a form that had already been submitted, is there a way to make it obvious what part of the form has actually been changed? 

i.e change font colour 

I am not sure if I understood your question correctly, do you want to see the version history of what changes have you made in your Form. If yes, then you may refer to these helpful guide:

https://www.jotform.com/help/294-How-to-View-Form-Revision-History

Is the Font color changes are not getting reflected in your Form in the preview?

Looking forward to your response.

Thanks.