As I was walking past a bowed psaltery in progress, I noticed an interesting phenomenon with the wood.

Light tends to reflect off of the wood in different ways depending on the orientation of the wood. So, two bookmatched panels, which are basically identical in color and grain pattern, can look different because they are oriented in different directions from each other.

Check it out:

In this picture, the upper right-hand side looks darker, and the top left side is light. (Along with a checker-board type effect with light/dark areas below each of the respective sides.)

But coming from a different angle, the Spruce top now reveals the opposite: the side which used to be dark is now light, and the light side is now darker.