Vermilion from cinnabar was an incredibly vivid red—almost blinding when it caught the sun on armor. Red, especially at that saturation, triggers the amygdala right away, so soldiers would feel an instinctive alertness, almost like a primal warning that danger is close. On the battlefield that meant the enemy’s brains were on high‑alert mode, their heart rates spiking, making them more prone to panic or hasty retreats. Plus, red is linked to blood and life‑threat, so seeing a knight’s armor glow like fresh blood could psychologically suggest lethal power—think of it as the medieval version of a “warning light.” The pigment itself was a form of mercury sulfide, so it also had a metallic luster that made the armor look almost other‑worldly, adding to the intimidation factor. In short, the hue was a deliberate psychological weapon that leveraged our innate reaction to intense red to keep foes guessing and on edge.