The dark tip to the bill indicates that this is an immature. This is the smaller nominate race found throughout much of North America, Europe and Africa. It is believed to have reached South America naturally from Africa and spread through the Americas taking advantage of clearing for cattle ranching. It 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. They feed primarily on insects kicked up by livestock.
This species is generally uncommon in Northern California 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.
Digiscoped with Panasonic DMC-LX5 | Nikon FieldScope III | 30XWA | hand-held (no adapter).
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