Because of humankind’s long close association with horses, horse coloration has a very specific and complex vocabulary (as any fan of wild west literature could attest). One of the most interesting horse colors is grullo a dun color characterized by gray body hair. Grullo gray can be either tan gray or mouse colored.
Grullo horses have bodies which are lighter in hue than their tails and manes. They also often have primitive markings such as stripes, spots, and stipples. Some grullo horses even have striped legs as though they were zebras or quaggas.
Grullo is of interest as an ancestral coloration of wild horses. The tarpan (Equus ferus ferus), an extinct subspecies of wild horse from Eurasia was believed to have grullo coloring. The last tarpan died in captivity in Russia in 1909, but mad attempts to recreate it through selective breeding have resulted in the primitive looking Heck horse (a breed of horse which tend to be grullo). Additionally many small harry northern horses like Norwegian Fjord horses and Welsh ponies tend to be grullo. Look at how cute they are!