nZ or ZZ

Silver is a gene that affects the mane and tail of the horse, creating a 'silver' hue. On occasion the horse can have dark at their roots but ultimately the tail will usually be either one or two colors. 

ngul or gulgul

Gulastra Plume is a gene that affects only the tail of the horse. It works similar to silver, creating either a gradient or turning the tail completely silver. Like silver the roots can stay dark. This gene only expresses when dominant.