This one actually has something to do with Mark Bittman

I almost keeled over last week when MB posted something on his blog about Mexico City open air markets.
Apparently MB was in the DF recently (it might have been as recently as last week when I was there!!! - omg I cannot believe we did not bump into each other!). He went to a traditional open air market, the kind of mercado sobre ruedas )literally: market on wheels) that sets up once a week in every Mexico City neighborhood. Sunday is "día de mercado" in small towns, but Mexico City was never a small town, so every day is market day somewhere in that monster of a city.
This is not something MB knew when he wrote the post, and clearly his DF guides are guilty of not explaining to him that open air markets are as democratic and popular as tacos - everyone can afford them, everyone likes them and everybody relies on them. Unlike the US trend, where open air market = farmer's market = expensive/organic/local whatever, shopping in the street and buying from if not a farmer, at least someone who is a few steps closer to the vegetable you are buying than the supermarket around the corner is a perfectly normal every day activity.
And very often, the plastic bags your pound of tomatoes will come in are brightly hued, as are the tarps that cover the stands in the market. In fact, if you fly into Mexico City during the day, you can tell which neighborhood has a mercado that day by the bright yellow, bright pink and bright orange tarps that cover an entire block or two. It looks amazing from above.
And it smells even better when you are in it. Apart from vegetables and fruit (including MB's favorite, the mamey, which he unfortunately insist on calling a mamay), there's always a huge flower stand or two, infusing the square footage around them in the smell of marigold and azuzenas, roses and carnations. These stands are always brightest and biggest. And then there is the juice stand, and the taco stand and the medicinal herb stand. Plus whatever other needs must be met that week (piñatas, flower pots, baskets, light fixtures).
Mexican markets are a microcosm of Mexico - everything is available and everything is possible, you just need to be flexible and know the local jargon, and you shall get it all, eventually.
For MB's post, click here.