For tuna, the color reflects the fat content. Maguro/akami ("red flesh") is red & lean, and stays that way even if frozen. Chutoro is pink & fattier, while oto

For tuna, the color reflects the fat content. Maguro/akami ("red flesh") is red & lean, and stays that way even if frozen. Chutoro is pink & fattier, while otoro is light pink & extremely fatty. (It was fed to cats in the olden das, before tastes changed and it became an expensive delicacy.) Brown tuna has oxidised and you should steer clear of it, but this is not a common sight these days. Also, essentially all commercially sold tuna has been flash-frozen, because it's caught in the deep ocean. That famous tuna auction in Tsukiji? All frozen, every last one. FWIW, I've had locally caught, non-frozen tuna a couple of times. It's good, but while the texture is different, it's just firmer, not necessarily better.