I'm sure the answer to this is "conditional formatting", but I don't know how
to get it to work...

I have a spreadsheet I use to track employee training on procedures. One
column lists the date the procedure is active and another column lists the
date an employees training on it. When the procedure changes I update the
appropriate cell in the first column to show the new date. I want the cell
containing the employee training date to change color if the dates don't
match. How would I do that?