spring creek brown trout

It's always fascinating to see spring creek fish. They are usually dark and very colorful. A typical dark type brown trout from a highly vegetated spring creek. Animal coloration/pigmentation originated from different mechanisms, the most common one would be the melanism from black melanin pigments. the second common one would be the orange color from the carotenoid pigmentation. For some brown trout from spring creeks, they are frequently showing the dark and deep orange belly coloration, particularly during the breeding season. I am not sure if someone have studied the skin coloration of those dark brown trout, but I am sure I would love to do it in the near future. One of the direction I am thinking would be linked the fish diet to the pigmentation. I suspect those fish eat a lot of fresh water crustacean shrimp and scuds which can contribute to the pink/orange coloration... but this is just my guess, of course.