Many people misunderstand otoro because they are served other parts of the fish (substitutes) and told its otoro, or served other fish that is fatty and resembles otoro. At least this happens outside of Japan and here I imagine infrequently but perhaps once in a while tourists are fooled. This cut looked almost like beef and had a pinkish color until it was swiped with nikiri and transformed. The tuna after being purchased goes through its own changes via fermenting, etc and changes color.