How to you stop Conditional Formating from actioning due dates when completed

I have 'Conditional Formating' on a Column with meeting due dates so that they turn yellow when the current date is 28 days before each due date, turn orange when 14 days before each due date and turn red on or past each due date.

I have added another column so that when meetings have been completed, the date is entered.

How do I stop the 'Conditional formating' from actioning when a date has been put in the completed column?

Can anyone help?

Sorry - I haven't explained very well.
I have meeting due dates in column D which has been 'Conditionally Formated' to highlight 3 different colours at 28 days, 14 days and overdue, I have other info in other columns in between Column D and my new column G so that staff can enter dates of when the meetings have been completed.

If the meetings have been completed before the due datesI don't need the 'Conditional Format' to highlight the due dates in Column D, can the 'conditional formating' be stopped from actioning the column D?

Hi Roger I am having problems attaching my example. Whenever I click on the attachment button It says 'error on page' at the bottom of the page so I am giving you the fromat for the 'Due Date column-

1st - 'Cell Value' 'Equal To' ="Null" / no colour designated.
2nd - 'Cell contains a blank' / no colour designated.
3rd - D4>=TODAY()+4*7 / colour yellow
4th - D4>=TODAY()+2*7 / colour orange
5th - D4<=TODAY()+7 / colour red

There is no formating on the completed column

Yours
Jo