|Let's say your date (12/12/2007) is in E4.|
1 - From the Ribbon select Home - Styles - Conditional Formatting,
2 - From the drop down select 'Manage Rules' and select 'New Rule'
3 - In the dialog box select the last item in the list 'Use a formula to determine which cells to format'
4 - Enter the formulas below as a 3 separate Rules, clicking the format button then 'Fill' Tab and selecting a color for each Rule:
=IF(TODAY()>$E$4+1095,TRUE,FALSE) Format with Red
=IF(TODAY()-$E$4>182,TRUE,FALSE) Format as Green
=IF(TODAY()-$E$4<182,TRUE,FALSE) Format as Orange
Each of these formula will use the TODAY() function (which always returns the current system date) to compare the current date to the date in E4.
1095 is three years worth of "days" (3 * 365) so if "today" is greater than E4 + 3 years, the cell will turn Red.
The other formulas use 182, which is approximately 6 months. Adjust as desired.