Conditional Formatting Main Report based on Field from Subreport

I'm using Crystal Reports XI.

I have a report that has one Subreport based on a different data set which sits in a group header of the main report.

The subreport is looking at a different data source for the same "clients" and "providers

"The main report and subreport share two similar fields; Provider ID and Client ID.

The subreport is linked to the Main report on Provider ID.

The main report's data set sometimes shows additional Clients in the details section for a provider that aren't in the subreport. What I would like to do is change the background color of the details section of the main report if that particular client isn't in the subreport for that provider.

Can this be done in Crystal? If so, any help in doing so would be appreciated.