Have you ever wondered why fish come in a rainbow of colors?

An NPR report breaks down why red yellowfin tuna flesh is completely distinct from blue lingcod or other fish.

While color is influenced by genetics, it's also about the fish's lifestyle. Because the red yellowfin tuna has to be a strong swimmer, its muscles need a lot of oxygen, bringing in a protein that doubles as a pigment.

"It's true of land animals, too: If they're walking around a lot, they'll have more myoglobin and their meat will be darker," Bruce Collette, a zoologist with the National Marine Fisheries Service, told NPR's The Salt.

Myoglobin is the protein that stores oxygen to keep muscles moving. It acts as a pigment in mako sharks and swordfish as well, making their flesh a "pinkish-red."

NPR warns fish fans to watch for tuna that seems too good to be true--if the flesh is unrealistically cherry-red, it may have been exposed to carbon monoxide gas to be restored after fading to brown. Artificially freshening fish with this method is illegal in some countries, including Singapore, but not in the U.S.

Blue lingcod is more of a mystery since biologists still aren't sure how the bright color gets into the flesh of the West Coast fish. It is believed that biliverdin, a bile pigment, makes the bottom-dwelling species blue.

White fish flesh often means the species has a quieter lifestyle. Pacific halibut is translucent prior to cooking and then turns white. The fish species has long muscles that sustain it for short bursts of activity, but halibut are usually found swimming slowly or resting on the ocean floor.

For salmon, the bright pinky-orange color signifies both their diet and genetic traits. The orange comes from the krill that are part of the salmon's diet. Pigments called carotenoids, which are found in krill, turn the salmon's flesh orange due to a "color gene" in the fish's makeup. 

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