With their rainbow colors and odd shapes and sizes, the appeal of heirloom tomatoes is undeniable. But more than just a pretty face, these darlings of the summer farmers market also represent diversity and freedom in our food supply.

"People ask me, 'Is this heirloom or hybrid?'" says farmer Bill Crepps of the Winters, California farm Everything Under the Sun. "You can tell that there's something they don't like about the word 'hybrid.'"

Crepps, who grows more than 20 varieties of tomatoes, recognizes the allure of heirlooms. But he also thinks hybrids have received a bad rap, in part because people confuse them with genetically engineered (or GMO) plants. He believes that hybrids hold an important place on small, diverse farms. "I grow heirlooms for their variety, but I rely on hybrids for their disease resistance," he says.