Conditional formatting, color cell if empty and date is passed

Trivium013 In I:K you coloured all dates in the past green, excluding blanks. Probably something like this: =AND($I4<TODAY(),$I4<>"")

For columns N:P, I believe you need three separate rules:

Rule 1: =$N4>=TODAY() , no formatting, stop if true

Rule 2: =AND($N4<TODAY(),$N4<>"") , green

Rule 3: =AND($I4<TODAY(),$I4<>"") , red

Rule 1 captures next appointment made in the future and stops further evaluation

Rule 2 captures next appointment made but already passed, excluding blanks

Rule 3 captures past appointment in the previous block of appointments and no next appointment made yet and excluding blanks

You can apply the same logic to the next block of appointments.

Demonstrated in the attached file.