[Anjin]

No, the mirror is on a stick and doesn't move. When Tim is looking down at the mirror from above he can see the reflected image he wants to paint, and also the paint surface he is going to paint on. He keeps adding color until the edge of the mirror disappears at which point he knows that he got the color on the surface to match the color in real life.

Here's a screenshot. The mirror is on the top, and the painting surface is below: http://i.imgur.com/Uk7vSQ5.png

Or on the painting of his father-in-law: http://i.imgur.com/WP2ls3A.png