The information is for use at own risk.
Bloody marks are areas of pigmenting that never grey out on a grey horse.
They can be quite extensive or they can be very small. The genetic mechanism is again unknown but is unique to Arabians and said to show antique or ancient blood. The occasionally whitebody spotting that shows up in Arabs and leg runs, white leg markings that continue in a streak up the leg sometimes past the hock, are also said to show old blood and may be related to the Sb sabino gene or it may be something unique. If related to the sabino gene it may explain the very rare parti-colored horses that are occassionally born to purebred Arabian parents.