The convention the author of this blog follows is to use "sabino" (lowercase with no number) as the generic term for those patterns traditionally referred to in this way. The reasoning for that is presented in this post.
Readers would not need to wander far online to encounter someone correcting them for calling their horse’s color sabino if Sabino-1 does not occur in the breed. This erasure of sabino as a word to describe a broad group of patterns, or the phenotypes they produce, is problematic for a number of reasons.
The proposed replacement for the remaining patterns for this group (white spotting) is not exclusive to them, or even to pinto patterns.
Years have been spent educating the equestrian community about these patterns using the term. To insist that it not be used for patterns that are part of the same group and that in many cases are visually indistinguishable, creates mistrust and undermines credibility. It is not helpful to create the impression that what is taught today will change tomorrow.
It creates a line between Sabino-1 and the related patterns that is not reflected in the behavior of the patterns themselves.
It does not accurately reflect the use of the term in the current literature.
To that last point, these quotes come from two recent publications on horse color. As with the other terms in use for these patterns, I encourage readers who have access to read the entirety of these books to get the full sense of the context.
From the fourth edition of Equine Color Genetics (P. Sponenberg and R. Bellone, 2017)
One mutation leading to sabino horses is called sabino-1. This was the first of the sabino patterns to have its genetic cause documented… (p.191) Investigations into the occurrence of white or nearly white patterns in several breeds have documented 25 different mutations at the KIT locus (including Sb1 and W1), and this number is certain to go up even more. These additional alleles all cause different levels of sabino expression… These are a family of mutations all at a single locus, and they have overlapping phenotypes. (p.194-5) The documentation of multiple genetic controls for the sabino pattern points to the fact that the sabino classification does indeed include a handful of distinct patterns. In that sense, sabino is now serving as a catchall designation for distinct genetic mechanisms. (p.197)
From the second edition of Horse Genetics (E. Bailey and S. A. Brooks, 2013)
The focus of this section is one particular sabino pattern, found in a variety of horse breeds… All horses found to have this mutation have a sabino pattern, but the mutation is not present among Clydesdale horses, or among other horses exhibiting another sabino pattern, demonstrating there are multiple pathways to producing this phenotype. (p.59) The allele responsible for the one type of sabino pattern (Sb1) described here was discovered within the KIT gene… (p.60)
It should be noted, however, that some authors do use sabino without its numerical designation. This is particularly true in papers that discuss colors in ancient remains, where Sabino-1 is (at the moment) the only pattern from this group that is likely to be relevant. In that context, wading into the complexity of sabino phenotypes is not necessary. For the purposes of this blog, though, the more recently arisen W alleles are relevant, so the distinction between sabino the phenotype and Sabino-1 the allele is important.