Sabino is currently an umbrella descriptive term encompassing the white patterns White Spotting (W) and Sabino1 (SB1). Sabino is generally characterized by high white, belly spots, all white, wide blazes, "chrome", lacy white spots, body spotting that is not one of the other pinto patterns, and etc. There is a lot of ongoing research and discoveries currently going on in sabino patterns and knowledge is changing rapidly.
White Spotting (W) is a dominant pattern of which 20 types have been found thus far and there are likely many more. White Spotting encompasses an extremely large expression of patterns. Expression ranges from a solid white coat, a near white coat, roan appearing sabino, the traditional description of a sabino, and minimally marked. Interactions between multiple white spotting patterns can have varied outcomes. White spotting generally has dark eyes, but blue or partially blue eyes are not uncommon. Many of white spotting mutations are homozygous lethals, but many others are not. W20 appears to be widespread and creates minimal white markings. Chincoteagues likely have some type of white spotting.
Tests for 20 types of white spotting are available. There are likely many more types of white spotting, so many they will likely never all be found. White spotting is found on the KIT gene. KIT is well known to mutate frequently which results in new white patterns. The current testable white spottings with the founding breed:
Sabino 1 (SB1) is an incomplete dominant. Horses that are all white with pink skin are homozygous for sabino1. Horses that are particolored are heterozygous for SB1. SB1 horses mostly have dark eyes, but blue eyes are not uncommon. SB1 is located on the KIT gene. There is a test available for sabino1. Based upon the consistent nature and fairly consistent appearance of sabino1 it does not appear to be present in Chincoteagues.
There are also white patterns in multiple breeds that fit the umbrella description of sabino that have not been found on the KIT gene, on which both White Spotting and Sabino1 are both found.
It is not known when sabino was introduced into Chincoteagues. The early ponies had minimal markings so it was either introduced through outcrossing or appeared through a new W mutation. If it was introduced it was likely through the outcrossing that also brought in tobiano and splash.
The ponies below have not been tested for sabino1 or any form of white spotting, and some of their markings may be actually as a result of splash. However, their white markings fit some of the common descriptions of sabino.