The red/black or extension gene (MC1R) controls the production of red pigment (i.e. to produce the chestnut coat colour) vs black pigment (i.e. to produce black or bay/brown coat colours). All chestnut and chestnut-based horses such as palominos have two copies of the red gene. Other horses can have either one copy of red and one copy of black, or two copies of black.
If your horse or pony is bay, brown or black, you can use genetic testing to check whether they have one vs two copies of the version of this gene that produces black pigment. Horses that have no red gene cannot produce chestnut offspring.
Gene or region and technical reference
Gene: MC1R (causative). Reference: Marklund et al. (1996)
E. Test developed using animal controls.
e. Test developed using animal cases.
Like all chestnuts, this chestnut brumby has two copies of the red gene.