So it's both genetics and diet.
Let me explain;
The compound in crustaceans that causes the meat in salmonoids to be red is called astaxanthin.
If any species of salmon or rainbow trout does not eat an organisim that contains astaxantin, the meat won't be red.
This explains white meat hatchery raise trout that from the hatchery have white meat that then turns red after eating crustaceans, or the immature winter kings that have a diet heavy in herring/candle fish, etc.
The writer of the article goes off base a little when he say the common, but false deit theory, is that, since iodine is red, and crustaceans have iodine, then that is waht causes red meat. I have never heard this explanation. The writer needs to just stick with what the scientists say, which is:
"White kings, however, lack the gene required to metabolize pigments from their foods into their muscles leaving the flesh neutrally white.
It?s not what they eat that determines the color of a salmon?s fillet, it?s if they can metabolize the pigments into muscle coloration and that ability is determined by pure genetics." (but
it is what they eat that causes coloration; astaxanthin}.
However, if the fish is not eating organisms that contain the pigments that cause the coloration, that fish won't be red; whether is has the gene or not.
This question/situation is sort of like an LSAT question. All salmon that lack the gene to metabolize astaxanthin will always be white meated, but not all salmon that have the gene to be red meated, will necessarily always have red meat.