For some reason, I'd always associated the change of color at the center seam, when the top is moved side to side with runout. In Steve's post, it sounds as if he's referring to the grain direction at the center seam, and that could well be true, and what I see as a changing color at the center seam might be caused by varying grain direction. I'd never considered that.
I happen to own a couple of guitars that have very high quality tops. If you look at the seam on those guitars, you look from one angle and one side looks darker than the other, but if you roll the guitar to the other side, the half that was light is now dark, and the half that was dark is now light. If you look at the grain patterns in the wood, both sides match perfectly, so there no doubt they were cut book matched, grain is almost identical for both sides, so what causes the different shades on either side of the center seam.
West