How can I change cell color based on the date that the text inside of it was inputted?

Hi there,

I am in charge of scheduling employees for shifts on five different shops. Every week, I open the previous week's schedule (Week 1), and do a "Save As," putting a new date on it (Week 2). Usually, I keep all of Week 1's data, and just make a few tweaks appropriate to Week 2. I would like for the Week 2 changes to be highlighted in a different color, so that I know at one glance that I've made all of the tweaks that I have to (there are 25 employees and over 100 shifts to fill so the spreadsheet is rather complicated).

When Week 3 comes along, I would love to do the same thing: "Save As" the Week 2 schedule into Week 3, and have all of the data from Week 2 be one color, with the tweaks made for Week 3 a separate color. In other words, I no longer need to differentiate Week 1 from Week 2, I just need to differentiate Week 2 from Week 3.

Keep in mind that none of the cells actually have dates in them--just names of people.

Is there any way to do this? I would LOVE to hear it if there was! Would make my life so much easier!!!

Thanks
Nathalie