Conditional Formatting for Dates in Excel

Hi -

I'm trying to create a formula that will change the color of a cell based on a date in 2 and 4 week intervals.  I want to be able to enter in a date (which would start green) and then 2 weeks from that date entered turn yellow, then two weeks from that date, turn red.  What I don't want it to do is base the color changes on today's date, but on the date actually entered in the cell.  

The formula I have now changes the colors based on the current date (TODAY) but not on the date that was actually entered in the spreadsheet.  

Is there a way to change the colors based on the date entered in the column and not today's date?  Once the cycle is complete, I want to be able to enter in a new date, and have the same process repeat.

Basically I have a list of inventory and want to know where it is in the 4 week cycle so that it can be cleaned, and then re-entered back into inventory to go through the 4 week cycle yet again.

Thanks.