Seal brown is a shade of bay, once believed to be an allele of the agouti (ASIP) gene. For a while, a DNA test existed for this particular shade. Unfortunately, no scientific papers were published and when DNA tests returned with inconclusive results, the test was withdrawn. As a result, seal brown is once again a phenotype of bay, and there is no evidence it is a separate genotype.
It is, however, part of this game as part of agouti, but it can not be tested for specifically.
Horses with a seal brown phenotype are generally dark, sometimes appearing to be black. However, areas around the muzzle, eye, belly and other soft parts are lighter coloured, often more yellowish. The back and crest of the neck are (nearly) black, and these dark hairs move downwards until they meet the lighter areas. Every time a horse sheds, it can appear to be slightly darker or lighter than the previous season.
Seal brown is sometimes prone to some very pronounced dappling.
The colour was believed to be an allele of the agouti gene, which is also responsible for bay (AA or A) and black (Aa or just a). Seal brown was specifically denoted as At and supposed to be dominant over a, but recessive to A. This would give the following results:
- Aa/Aa = black
- AAt/Aa = seal brown
- AAt/AAt = seal brown
- AA/Aa = bay
- AA/AAt = bay
- AA/AA = bay