Like Pokémon, there are also monsters with a different color than usual in Invizimals. In Pokémon, they are called shinies. In Invizimals, they're called mutants.

Grey Salma seems to be the equivalent of the red Gyarados, since it's one that has a 100% chance of being a mutant. Normal Salmas are purple with green eye markings. While playing the game, you meet this guy who wants a Roarhide Max (final evolution of Roarhide). When you get one, you battle him and he uses the mutant Salma. If you win, he gives it to you.