Base coat colours
Coat colour dilutions
Genetic disorder tests
The dun coat colour in horses dilutes both red and black pigment by limiting the distribution of pigment granules to a small part of the hair shaft. This dilution is accompanied by darker undiluted markings that can include a dorsal stripe (most commonly), leg barring, dark ear tips, and shoulder bars. The face and points of dun horses are also usually darker than their bodies.
In contrast, the coat colour and markings associated with d1 reflect what is commonly referred to as counter-shading.These horses are expected to have a dorsal stripe and possibly other markings usually associated with dun. Horses that are positive for d1 but not dun are NOT dun.
Our information and terminology is based on the sequences and content in Imsland et al. (2016): doi:10.1038/ng.3475