Pokemon often differ slightly in color in response to climate – the Orange Archipelago in particular is known for the vibrant colors of its tropically adapted wildlife - and one in thousands in any climate will be born with a strange and shining color scheme. Shellos in most climates show a variation of color over a surprisingly small region; for instance, Sinnoh's seas are divided between pink and blue Shellos, while Hoenn's were primarily purple before extinction, although some bays had pink Shellos with yellow-green fins. This alone is a smaller number of shades than a single Kecleon or Deerling, both of which will change color over their lifetimes, but Shellos once had a much wider range than Sinnoh.

In Kanto and Johto in particular, the lakes and rivers around every town had a unique color of Shellos, and new towns were typically named by the color of Shellos in the area. These colors became points of pride, and building roofs were often painted in colors approximating those of their town pokemon. The waters south of Pallet Town had Shellos of every color, and kept this distinction over generations. This is because Pallet Town never had a native Shellos population, only a large variety of Shellos from around the region born at the town's large pokemon research lab and released into the wild, so the diversity of shades has maintained itself instead of blending into a new, mixed color.

Today, only Pallet Town maintains a population of Shellos, for its environment alone has remained free from the chemical pollution which has wiped out their counterparts. Trainers today trade for pokemon from far and wide, but still leave their pokemon with the local pokemon professor, and their descendants there join a population which has replenished itself this way for generations.