He's right, the bright lines will be EGT's, the blanked out are CHT's. Most of these instruments don't have actual values attached to them, so you're just going off of what you see. The good news is that since it's not turbo-charged, you really don't have to worry about cooking some cylinders by learning the system. Just play around with a variety of mixture settings, I do them by sound/feel first, then start modifying the mixture and watching the guages. You'll eventually see a pattern. Also watch the values on climb vs. descent, that will really highlight the CHT values for you.