At the cost of duplicating my other comment, it fits here perfectly:
I hate to cry conspiracy theory, but I really do think that American culture in particular has been groomed to think and eat this way by food suppliers. When you can color / bleach something, you can hide flaws.
Not sure where purple tomatoes would fall. Some googling turns up anthocyanin as the pigment, and Wikipedia says it's water-soluble (so would leach out if the fruit is boiled and the water not retained), and changes color based on pH.
I tend to consider conspiracy theories a last resort. It is not that they are never true, just that reaching for them first is a mental crutch. In this case, I would suggest that given the importance of food, one would rather expect evolutionary considerations to dominate how we feel about food colorations. It may be true that making food "look good" can be used to hide flaws, but I seriously doubt the concept of "looking good" comes from training. I would imagine it mostly comes from genes and common-sense-type-training.
(I assert this without proof, which is why I mentioned my conspiracy-theory metric. My point is that I don't see a need for the conspiracy theory choice here.)
'Tis just speculation, though. There are plenty of weird / weirder things in the world.