How to get excel to ignore a blank cell

Aug 4, 2014
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Hello Internet,

so im having a problem with an excel spreadsheet. i have a bunch of expiry dates on my spreadsheet and when it has less than 30 days to expire the column next to it (which has how many days are left) turns RED. However when it has expired it goes clear instead of staying red. not all of the entries have expiry dates so I don't want the blank ones to turn red. however this happens when i set the value to turn red when below a value of 0. So how do i get it it to ignore if there is no expiry date?

Thanks for any help in advance.