It almost seems counter-intuitive for the idea of growing tomatoes, but sunshine is a double-edged sword. Tomato fruits actually need to be shaded somewhat by foliage, otherwise the result is the yellowing shown here, or even outright sun-scald, which has a bruising, destructive effect on the fruit.

Speaking of double-edged swords, in the Lewis Ginter Community Kitchen Garden we try to keep up with the sprawling tomato vines by tying the growth to stakes to keep the fruit up off the ground. However, as a byproduct we sometimes end up exposing the fruit inadvertently, until the foliage repositions itself naturally.