You may have already found the solution. If not, you may try
- select F11 cell
- click Home tab in Ribbon
- click Conditional Formatting, select New Rule.
- click Use a formula to determine which cells to format.
- in the textbox of Edit the Rule Description, type
=E11=""
- click Format button to apply the format that you want
- click OK button in Format Cells dialog. Click OK button in New Formatting Rule dialog.
- done.
