Report Designer, Expressions? or Conditional Formatting?

Hi,

I need some help with Report Designer, I am currently trying to make some alterations to a report that was created that displays a list of all of the outstanding PO's on our system and I would like to try and get the POPOrderReturns.RequestedDeliveryDate colour coded based on whether the purchase order has been received etc and I am not sure if I need to change the expression or use conditional formatting. 

Basically I would need that field to display in red if that RequestedDeliveryDate is already past the current date of where the report is run (so based on the current date) or green if its still within date. I am not sure of the syntax of the conditional formatting if that's the way to go. I kind of understand the logic, but I am not sure how to apply it in this case. I have tried searching for an answer, but there doesn't seem to be a lot of free information out there about it. 

Can anyone help?

Cheers.