I am growing "Celebrity" tomato plants in full sun in fertile soil. The foliage is healthy, the plants large, and the fruit plentiful. The problem is the condition of the fruit. I can see a spotty discoloration on the shoulder of the tomato and when I cut into the tomato, this discoloration runs throughout the interior. So instead of getting a uniform "tomato red" color on the inside, I am seeing splotches of yellow and red. The bottom half of the tomato does not seem to be as affected as the top half. How can I correct this issue?