The Atlantic:

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.

It’s the “pigmenting,” to use feed industry parlance, that really matters, letting salmon farmers determine how red their fillets will be. (Thanks to a 2003 lawsuit, they have to alert customers to the fact of “added” coloring.)

Si asumes que una gran parte del salmón que consumes es de piscifactoría, entonces has de asumir que su color salmón es debido a colorantes.