Hi and welcome to the board!!
Not sure what you really want, but it should be something like 1 of these
Conditional Formatting>Formula Is option
Code:
=($D1)*($D1<=Today()-180) or
=($D1)*($D1>=Today()-180)
Note the use of mixed Absolute/Relative notations. This is so the formatting can be extended down Column "D" . Adjust as needed
lenze