Anonymous wrote:

Farmed salmon, including Costo's the last time I looked, has food coloring to make it look "salmon color." Without it, it's grey.

The color isn't applied straight to the fish. It's added to their food. Salmon eat something that has a lot of caratene in it (krill, I think, I'm not sure) that naturally turns their flesh pink/orange. When they're farmed, they eat something else, but a carotene additive is added to their feed to give them that color.

http://www.washingtonpost.com/lifestyle/food/why-farmed-salmon-is-becoming-a-viable-alternative-to-wild-caught/2013/09/23/aaff33ca-1cbf-11e3-8685-5021e0c41964_story.html

http://www.washingtonpost.com/lifestyle/food/farmed-vs-wild-salmon-can-you-taste-the-difference/2013/09/23/3a2650a2-1fcb-11e3-8459-657e0c72fec8_story.html