Change cell color if content changes

You can use Conditional formatting.
Select the range and from the Home Ribbon select conditional formatting
Select Highlight cell rules
Choose Equal to
And in the dialog type the word that you want to check for.
Change the formatting to whatever you choose.

Actually rethinking your question...conditional formatting cannot check for if the cell changes (only if a value equals (or does not equal) something).
You will need code to check for ANY type of value change...not just one that meets a set condition.

I will set up an example for you...

Have a look at this sample workbook.
It has some basic code that will capture value changes in cells A1:A10 only.

To see/modify the code, right click on the sheet tab and choose View Code.