Conditional color formating in SSRS 2005

Hi

I have a report with customers bill amount and bill date. The customers have to pay within a grace period of 21 days after bill date

I want to conditionally format the bill_date column so that when the number of days after the 21 days grace period is within 7 days then no color,30 days then blue, 61-90 days then Red

Thanks a lot

Please very urgent