James Nienhuis is a professor in the Department of Horticulture at the University of Wisconsin.

Why is a watermelon red on the inside or a carrot orange? Why are they a color at all?

It could be involved with pollination, attraction of herbivores or dissuasion of herbivores. But really the carotenoids -- the yellows, the oranges and the reds -- are there for light, for photosynthesis.

Think about this for a moment: If the carotenoids are there for light absorption, I think most carrots grow underground. So what the heck are they doing there becoming orange when they can't even see the light? The watermelon, if I'm not mistaken, it's probably pretty dark inside there. Why would they become a bright red?

The answer to both of those questions is because human beings domesticated, selected and bred these crops. Those were the colors that were pleasing to us. That's why the watermelon -- those wonderful curlicues on the inside of that placental tissue -- that redness is all about us.

I think what we're most fascinated with is simply what it looked like 500 years ago in Renaissance art. Vegetables are perishable. We don't have the luxury that paleontologists have when they look at grains, in which the grains can be preserved for centuries in dry climates. They can look at the evolution of wheat from a little grain to a larger grain and the colors. Vegetables are perishable, so we don't have any indication of what they looked like 500 years ago because that was prior to my iPhone or the Kodak camera.

The only way we can really look at that recent history is through Renaissance art. Not only do you look at the painting, but you also look at the artist. By their names you can often determine if they're Dutch, or Italian or Flemish. You can also look at the dates. You can learn a lot about the history of vegetable domestication.

What fascinates me is you'll look at some of these paintings and you'll see that within 20 or 30 years after the discovery of the Americas, or the rediscovery of the Americas, you will find that there are tomatoes pictured in Italy or you will find squash pictured in Italy. Which is remarkable because those crops are native to the Americas. You see them so elegantly painted.

One of those [Giovanni] Stanchi paintings has a picture of a tomato on it. It has a tomato in it that looks like a Burpee Big Boy. I said, "Wow, talk about speed." You can tell that the Italians must have just been fascinated with this particular crop. They domesticated it very rapidly.