I object to using the term 'dye' with regard to farmed salmon. To me, a 'dye' implies something that is applied, like a stain or a paint but read here what the FDA says about food colors: http://www.cfsan.fda.gov/~lrd/colorfa... The following statement is at that website: "Butter has been colored yellow as far back as the 1300's." Butter is colored with carotene (sometimes called beta carotene). Carotene is a chemical in a class of chemicals called carotenoids and is found in high amounts in carrots. Why are there no posts about the dye in butter?
The thing that gives wild fish and farmed fish its color is carotenoids called astaxanthin (mostly) and canthaxanthin. Wild salmon get it from eating krill, small shrimp-like creatures; salmon cannot make their own astaxanthin or canthaxanthin. Farmed fish absorb astaxanthin and/or canthaxanthin from their feed because it's added to feed (fish meal) as the pure compounds. Besides freshness, colour is one of most important criteria for determining the marketability of salmon. Astaxanthin & canthaxanthin are not dyes or paints. Astaxanthin is a powerful antioxidant and a google search will show you that it is widely for sale as a 'neutraceutal' for human consumption.
The white chinook or white springs are a run of salmon that lack the ability to absorb carotenoid from their diet or so the muscle remains white even if they eat krill. I don't understand the arguments about the difference in taste of farmed fish vs wild fish. Farmed fish does taste different than the wild salmon because in general on the west coast, it is a different fish. I've never tasted wild Atlantic salmon and farmed fish are usually Atlantic salmon.