The above answer by Rahman did not work for me, it only highlighted empty cells when I selected a whole column. Here's what I did:

1. On the Home tab of the ribbon, select Conditional Formatting > New Rule Select 'Format only cells that contain'
2. Leave the first drop-down set to 'Cell Value'.
3. Select 'between' from the second drop down.
4. Enter =TODAY()+30 in the first box.
5. Enter =TODAY()-30 in the second box.
6. Click Format...
7. Activate the Fill tab and select a color.
8. Click OK