Need help creating a formula to highlight certain fields once another field has been popul

Once someone responds to a correspondence, I want certain data to be highlighted once the "response date" of my spreadsheet has been populated. That way I know that the correspondence cycle has been completed. I also want aging correspondence to be shown in multiple colors

For ex: I send invoices to my purchasing department. I populate the fields on my spreadsheet. It consist of the Buyers name, The vendor I am referring too, The date which I sent the request to solve the discrepancy, and finally a response date. I want fields to be "grayed" out once the "response date" has been populated. Also, I want things that are aging to go from green, yellow then red depending on how many days have lapsed.

Is this possible?