that's just how plants work

Yeah cause the sun stays in exactly one place. Otherwise this perfect line wouldn't be possible.
Apart from that, if your theory was true, we would see those EVERYWHERE.

here....you can make your own http://www.seattlepi.com/business/article/A-new-apple-to-tempt-Huskies-and-Cougars-fans-1159050.php

That only works on apples that are supposed to be red, and the non-exposed areas show up yellow, not granny-smith green.