Hello & Welcome to the Forum,
You can use CF...
Conditional Formatting- Highlight applicable range >> A1
- Home Tab >> Styles >> Conditional Formatting >> New Rule
- Select a Rule Type: Use a formula to determine which cells to format
- Edit the Rule Description: Format values where this formula is true: =LEN(A1)=0
- Format… [Number, Font, Border, Fill]
- OK >> OK