definitely diet - in most lakes or reservoirs there is fresh water shrimp, scuds, and crawdads and are very high in protien. Trout that have been in these systems for a year or two and are feeding mainly on these food sources will have a nice salmon color meat. Stockers will have white mushy meat due to the dog food they have been raised on, but once they are introduced to a high protien diet I would think their meat would get healthier. Most trout in rivers will have whiter meat and I don't know if it is because they mainly eat insects. Good Question, but definitely a diet related thing.