Not only does the humble tortilla have two distinct sides as you noted, each side has a specific function.
Although originally a Moche cullinary invention, the tortilla did not undergo any real development until shortly after the Inca conquered the Moche in around 1200 AD. The Moche did not cook the flour/water mixture, they allowed it to bake & dry in the sun and it was eaten as a thin, crisp bread. The Inca introduced the revolutionary step of “cooking” the tortilla. And, as with any new culture, affixed their own cultural devices to everything including the two subtly different sides of the tortilla. Cooking the tortilla rendered a more pliable bread which could be used for wrapping various other foods in neat packages–very handy for the long marches away from home seen by the armies of the new empire.
The darker side (first to be cooked) is called **Pachamama ** (Incan earth god), and it is this side which comes into contact with vegetables wrapped in the tortilla. The tougher surface helps the veggies retain moisture and keeps them fresh longer.
The lighter side is called **Inti ** (Incan Sun God), and this surface comes into contact with meats. This softer, more absorbent surface wicks moisture away from the contents and aides in curing the meat to some degree to prevent spoilage.
It is rumored that a minor civil uprising once began within the Inca empire as the result of one priest’s misbegotten insistence that the role of the sides be reversed. Furious at such blasphemy of the gods, troops were issued from Cuzco and the priest and his followers were executed without ceremony–a truly horrible death for an Inca. This is most likely a yarn, however.