So, I'm currently in a 2nd level drawing class and we've started using colors.

However, my theory up until this point has been that the shading (or highlighting) of something is done with a darker or lighter shade of the middle tone.

Apparently not. My art teacher (who paints and draws like an old master) was going on about using purples, reds, and yellows to create skin tone. It looked fantastic and realistic but I had NO idea what she meant. Cooler tones? Warmer tones? How do I recognize those when I'm drawing?