So distinctive is salmon’s orangey-pink hue that Crayola named a crayon after it. It’s an accurate representation of the flesh of wild salmon, but not that of farmed salmon, whose meat is naturally gray. Or at least, it would be, if salmon farmers didn’t spike their artificial diet with pink-ifying pellets.

Wild salmon get their ruddy shade by eating krill and shrimp, which contain a reddish-orange compound called astaxanthin. (That shrimp-heavy diet is also what turns flamingos pink.) The spectrum varies with the species: Since Alaska’s sockeye salmon are closer to the Bering Sea’s teeming krill, they’re the reddest of all. Salmon further south—Coho, king, and pink, for instance—eat relatively less krill and shrimp, giving them a lighter orange hue.

Like their wild cousins, farmed salmon come in a spectrum of pinks and oranges, depending on diet. But it’s the farmers—not the food chain—who determine the salmon’s color.

Since farm-raised salmon live in a pen, they’re fed kibble made from a hodgepodge that might include the oil and flesh of smaller fish (e.g. herring and anchovies), corn gluten, ground-up feathers, soybeans, chicken fat, and genetically engineered yeast.

An essential ingredient in these pellets is astaxanthin. Sometimes it’s made “naturally” through algae or pulverized crustaceans; other manufacturers synthesize the compound in a lab, using petrochemicals. While astaxanthin provides the salmon with some of the vitamins and antioxidants they’d get in the wild, salmon health isn’t the selling point.