Conditional Formatting

You may have already found the solution.  If not, you may try

1. select F11 cell
2. click Home tab in Ribbon
3. click Conditional Formatting, select New Rule.
4. click Use a formula to determine which cells to format.
5. in the textbox of Edit the Rule Description, type 

   =E11=""

6. click Format button to apply the format that you want
7. click OK button in Format Cells dialog. Click OK button in New Formatting Rule dialog.
8. done.