Excel 2003

Hello,
I know that you can use conditional formatting in excel 2003 to format a blank cell a certain color until text is entered into that same cell (at which is will change to the native color of the worksheet). My question is how can I do the same task if the cell in question is part of a drop down list using data validation? I've tried:
-Click in the field that you want the user to enter.
-Go to the top menu bar and click "Format"
-Click "Conditional Formatting"
-Under Condition 1 choose "Formula Is"
-Type =IsBlank(A1)
Note: Change A1 to be the cell that you are currently in
-Click the "Format" button and set the "Pattern" to be whatever you want it to be.

When the cell is blank it will be colored, but when any value is entered it will go back to the natural color.

This works great when it is an individual cell. However, I am running into trouble when trying to change the background highlighting when the cell is part of a drop down list that has multiple names to choose from. It stays the original native worksheet color and will not highlight the blank cell.
Any insight is greatly appreciated and Thanks in advance!