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Scientists have been examining the so-called dominant black color, which presumably may be controlled by a separate allele “E^D”. So far its location is not known, but in the opinion of some experts, it can be located in the Extension locus. Similar phenomenon of the inheritance of dominant black color has been described and studied in other animals.

The presence of this allele leads to the formation of black color even in genetically bay horses. As a result the carrier of this allele has a black color that cannot be distinguished from ordinary black horses (EE aa or Ee aa). Thus, allele “E^D” is epistatic with respect to allele “A.”

A foal with dominant black is similar to bay: brown with darker guard hair rather than the ashy color typical for ordinary black foals. The phenotype of the foal carrying dominant black becomes darker with age.

Next we will discuss color modifications determined by dilution mutations. Currently there are several separate dilution genes (for example, Cream, Silver, Champagne, Dun), and each has its own biochemical and molecular mechanism of action. More often it is possible to view color dilution as a weakening of pigmentation, and the molecular mechanisms of the action of some of these genes/mutations are still unclear.