Changing cell color dependent on date in a different cell

Please help. I created an spreadsheet in Excel 2010 for new hires form tracking. I now would like to have cells change colors to remind me that certain forms have not been turned in within 30 days of start date. I will like for cell to change to blue when the new hire have 15 days left to turn in forms. (from their start date). And cell to change to yellow when there is only 5 days to turn in forms. I know that this is something that can be done using conditional formatting but I cannot seem to get the right formulas to get this to work. Each row contain the new hire, their start dates and blank cells for each form needed. The columns list what forms are needed. After researching, all I can find are formulas that reflect from system date. Any help you can provide is greatly appreciated. NCnMD