This species invaded North America starting in the 1950's and is now common across the southern tier of the United States where it associates with grazing livestock, usually cattle. It is generally uncommon in Northern California and I was not expecting to see them standing on the back of sheep. Two races are recognized. This is presumably the widespread nominate race. A larger race with more extensive gold ornamental breeding plumes is found in Asia. The suggestion that the gold color comes from staining needs corroboration. Canon PowerShot SX50 HS.
Reference:
Telfair II, Raymond C.. (2006). Cattle Egret (Bubulcus ibis), The Birds of North America (P. G. Rodewald, Ed.). Ithaca: Cornell Lab of Ornithology; Retrieved from the Birds of North America: https://birdsna.org/Species-Account/bna/species/categr