Changing date field color based on difference in month

Hi,

I am creating a checklist with a "From Date" and an "To Date".

I have another field called "Completed Date". How do i script so that the "Completed Date" field will be filled with Red color if the difference between the "Completed Date" and the "To Date" is less than say 5 months.

I tried reading the "Working with Date and Time" guide but its too much for my understanding.

Thank you!!