Here is a short tutorial that shows how to make a rule that will change the display color of a powercopy. The syntax for the rule was worked out by Julie Flohr and her students at UIC. The next step is to work this into a knowledge pattern. The benefit of something like this is to give you real-time feedback based on a certain criteria that you set. As you change something, the display is updated.
Click the image to launch the video tutorial. It is 16 minutes long.