By Kevin Gray Between all of the different types and sub-types, there are hundreds of varieties of heirloom corn. But growing up in Colima on the west coast of Mexico, Olivia Lopez’s options were mostly limited to white and yellow, just like the typical American diet. “There was a movement in Mexico in the 1970s, when the government compromised to make corn cheaper because it’s one of the bases of Mexico’s diet,” she explains. As a result, mass-produced corn became the norm. Large farms began producing the same types of GMO corn, and smaller producers couldn’t compete. Lopez moved to Dallas an…