How To Automatically Update Field Using Date

I'm trying to update an excel document which has a list of employees on it along with their training. Most of the training for individuals needs refreshed in the next year so wanted the table to use the date and perhaps trigger a fill colour change once they are close to needing that training. here's an example

John Smith
course 1
Completed 01/05/10
Refresher required 01/05/14

Once we get a month or two before the required date, I would like the fill colour to change to highlight that they refresher training should be organised soon.