Formatting Pivot Table

[ASLittlefield]

I have built a pivot table to show the count of services render for each client in a program. (see below)

With the Rows being Client Name (redacted) and the columns being:
Service Year (date of service by year)
Service Month (date of service by month)
Service Type
Enroll date

And the Value = Count of Service

I have put in a format to highlight any month that the "Count of Service" is =0

BUT I need to gray-out any cells that are before when the client was enrolled, as each client has a different enroll date
I figured that it would that another formatting rule using a formula, but I am still a little new to pivots.
I would appreciate any and all advice.