Diet is what changes the flesh. Zooplankton, crayfish, adn other invertebrate eggs will change the flesh color. If fed hatchery food, benthic insects, minnows, the flesh will be white-(ish). Something to do with carotinoids. Caratinoid uptake by fish is controlled by at least two genes. One makes a carrier protien found in the blood, and the other is a transporter protein that allows the pigment to accumulate in muscle tissue. If either gene is absent, you get white meat.