Ancestral alleles are shown in grey and derived (non-ancestral) alleles are shown in blue. As a new positively-selected allele (red) rises to high frequency, nearby linked alleles on the chromosom ...

The merle allele takes the eumelanin and dilutes it into a shade of gray or blue. There are two major types of Blue Shelties. Blue merle Shelties will have gray, tan, and white double coats.