Science tells us that the rosy tint of a rhubarb pie is vital to its flavor. But this doesn't mean there's an innate relationship of deliciousness between pink and rhubarb—it merely suggests that we've grown accustomed to the pairing. Likewise, the red in red velvet cake might someday taste as natural and delicious as the yellow in butter, the brown in Pepsi, or the orange of oranges.
That's why chefs engage in all sorts of mischief to mask the natural colors of prepared food. We acidulate apples and artichokes to prevent brown stains, and shock our greens to keep them bright and zesty. Grenadine adds some red to a gray slop of poached strawberries; squid ink makes a beige risotto black; a few threads of saffron turn rice a jaunty yellow. Chef Thomas Keller feels no shame in admitting that he makes a flavorless colorant from ground-up spinach, parsley, and watercress, which he adds to herb sauces to "heighten visual impact." We're hardly inclined to keep our all-natural ingredients in their native states, and yet we shun artificial colors for being "fake."
At the same time, some of the world's most famous chefs experiment with industrial ingredients that let them alter the texture and shape of their foods beyond recognition. Ferran Adrià of Spain's El Bulli employs xanthan gum to give puréed mango the texture of an egg yolk. At WD-50 in New York, Wylie Dufresne uses transglutaminase (or "meat glue") to make noodles almost entirely of shrimp meat and chicken breasts into perfect spheres. It's easy to imagine how Adrià or Dufresne might use a pallet of chemical lakes to paint his foods to exquisite effect. But it seems like even these freewheeling molecular gastronomists stop short of artificial color. What are they afraid of?