Auto highlighting a cell when parameters are exceeded

I am working with a spread sheet requiring the results of cell b5 fall between 28% and 32%. If the formula result in b5 is outside the aforementioned limits, it makes the background or fill to become light red thereby alerting me to the disqualification. I should mention that this sheet was created by my predecessor several years ago and I have no way of requesting his/her input. I am attempting to apply this feature to several other cells which display formula results but am unable to activate the highlighting feature. When I select the cell b5, it will display the formula but nothing to indicate how to activate the highlighting feature. This is just an additional safeguard which I wish to implement. Any suggestions?

I will and thank you.