Although wild Corsola have not yet been spotted in western Sinnoh's many poorly-mapped swamps and lakes, many have speculated that the difference in color between the two types of Shellos and Gastrodon is due to the presence of Corsola in the western group's diet. Crushed Corsola provide a pink dye which looks remarkably like a Gastrodon's color, but this does not explain the brown shell, a weakness in the theory which many consider fatal.
It is not completely impossible; pink dye from Corsola was traded as far north as Sinnoh in antiquity, and perhaps some live specimens were given to a king by a rogue trader – rogue, for the pink dye was a source of great wealth and the pokemon it came from became a closely guarded secret. If the ruler lived in Western Sinnoh, Mount Coronet would block their spread east and Corsola multiply quickly anywhere they can grow. Yet it must be remembered that virtually every pink pokemon from Clefairy to Mew has been theorized at one time or another to use Corsola dye in its skin, for Corsola have long been associated with beauty. And this is not a Milotic's beauty, but a beauty which, like its dye, can be seized by humans. Corsola, being part rock-type, are inedible for humans and most pokemon (interestingly, Gastrodon are among the few exceptions) but in every age, a few foolish beauty seekers have broken their teeth trying.
Even today some skin care products tout the benefits of their Corsola-based formulas, claiming to give your skin a beautiful pinkish hue. Were they made from real Corsola, however, they would only cause massive itching. The dye does not create a soft and pleasant tint, but a bright pink which would make the unwitting user look more Mr. Mime than human.