What is the color of the passivation film on galvanized steel pipes?

The color of the passivation film primarily varies depending on the concentration of hexavalent chromium and the thickness of the film. When the concentration of hexavalent chromium is high, it appears red; when the concentration is low, it appears orange or yellow. Therefore, with different concentrations of hexavalent chromium, the passivation film exhibits various colors ranging from red to yellow. Since hexavalent chromium sometimes exhibits a purple hue, purple may also be mixed in with the colors ranging from red to yellow. Thin passivation films can exhibit iridescent colors due to light interference. Generally, the color of the passivation film on galvanized steel pipes is most commonly yellow.