How to highlight changed values after every refresh

You cannot detect each individual record change. I think you will need to have a "last refreshed data" and "current refreshed data" table and compare for differences. This will require some way to backup/copy the refreshed data so it becomes the last refreshed data. 

Or if your data source could add time stamps to each record and then you compare that timestamp to the refresh time, but that still means you need to know when the last refresh time was, which means a table keeping track of your scheduled refreshes, which would be an estimate. A refresh at 8am doesn't always happen at 8am depending on how many other reports you have refreshing then and the system's overall load. I've seen them launch as late as 15-20min later.