Leopard complex - sekelsta/horse-colors GitHub Wiki
The leopard complex gene is required to create appaloosa patterns. Horses with the leopard complex may be varnish roan, spotted blanket, snowcap, leopard, or fewspot patterned. Which pattern appears will depend on other genes, one of which is Pattern 1 (PATN1). Other unknown genes generally have a smaller effect on the pattern.
The white patterns created by the leopard complex and related genes can appear on top of any base color. When a pinto pattern is also present, the horse may be called a pintaloosa and will generally have more white than a horse with either pattern alone. For instance a tobiano leopard would have solid white areas and white areas with spots of color.
Pattern 1 causes leopard complex horses to have a blanket which usually covers about 60-100% of the body. When the blanket covers 100% of the body, it is no longer called a blanket but is simply the leopard pattern. Without Pattern 1, a leopard complex horse can have a blanket covering about 0-100% of the body. (If it covers 0% of the body, it's also not considered a blanket.) So, Pattern 1 causes the leopard and large blanket patterns, but those can also occur without it.
Health effects
The leopard complex gene causes congenital stationary night blindness (CSNB) when it is homozygous. In game, night blind horses will move slowly and carefully at night.
Leopard complex also increases the risk that a horse will have equine recurrent uveitis (ERU). In game, that means lower max health. There are thought to be other genetic risk factors for ERU (see here), possibly linked to the major histocompatibility complex (see here).