In southeast Alaska, the shell of M. trossulus is almost always black and dark blue. In warmer areas, like California, it is more often brown. Why?? This is to be an adaptation to temperature. The brown shells soak up less solar heat than darker black and blue shells. Thus, brown shells help southern species stay cooler. Conversely, darker shelled Alaskan individuals can soak up more rays and more heat…when and if the sun does shine! A few brown specimens most likely still exist in Southeast Alaskan populations due to mutation.