Varnish roan is not a result of the roan or the Gray gene, but part of the Appaloosa complex, based to some extent on the Leopard (Lp) gene. A horse may have varnish roan coloration in conjunction with other appaloosa patterns.
By adulthood, the Varnish Roan usually has a base coat of intermingled dark and white hairs, though more white hairs than dark, with mottled skin, color mainly on the cheeks of the face, and around the knees. The darker areas remain at bony points (on the face, usually in a distinct V on the bridge of the nose; on the cheeks, point of shoulder, elbows, knees, point of hips, hock) and it can be seasonal as well. Although classic roans are roan from birth, varnish roans are born with spots and "roan out" as they age. A horse's appearance can change almost completely, although the original markings are usually visible.
The pattern is not completely stable. The horse is born another color (usually another appaloosa pattern), and the Varnish pattern gradually overtakes it by adulthood. After the horse is mature, the coat color may lighten slightly when the horse has a long winter coat, and darken slightly in the summer when the winter coat sheds out. However, unlike the gray gene, the color does not get progressively lighter every year for the life of the horse, though it may look a bit different from year to year while the horse is young.