This adjective describes something sulfurous—having the color, smell, or properties of sulfur (brimstone). Classical usage applied it primarily to sulfurous waters and yellow-colored objects. John uses it in Revelation to describe the yellow breastplates of demonic cavalry, connecting them visually with the fire and brimstone proceeding from the horses' mouths. The term emphasizes both color (bright yellow) and association with the judgment-bringing substance sulfur, often paired with fire in biblical imagery of divine wrath.